How do I pull the updated information from a tkinter form?

[Steve]

#  With this program, I can read the information from
#  Specifications.txt file and display it on a form.
#  The user can then update/modify the fields. This is
#  all working fine and beeautifully...
#  
#  I now need to reverse the process and replace the
#  adjusted lines of data back into the Specifications.txt
#  file.  Fortunately, that code has already been
#  written .

#  What I cannot seem to do is to pull the adjusted
#  information from the form into variables, or a
#  list/array, so that can be used for the update to the file.

#  Suggestions for what to look up to study this
#  through will help.
#
#  Thank you
#  Steve
# ---------------------------------------------------------------

import tkinter as tk
from tkinter import ttk
import sys

ThisList = ["start"]

#===============================================================
def FillTheList():
   x=0
   ThisList = []
   with open("Specifications.txt", 'r') as infile:
     for lineEQN in infile: # loop to find each line in the file for that
dose
         if lineEQN[0:1] == "-": # Lines with "-" in space 1 have special
recognition for this form
           ListItem = lineEQN[1:6].strip() # Remove any spaces before and
after
           ThisList.append(ListItem) #Add the ListItem to ThisList
   return(ThisList)

#====================================================================
    
def EditDataByForm():
    window = tk.Tk()
    window.title("Python Tkinter Text Box")
    window.minsize(700,700) #height, width
    
    #===============================================================
    def GetLineByItem(DataType):  #get line by item in column 3 - 5
        #print("DataType = " + DataType)
        DataLetter = DataType[0:1] #Capture item letter ID for file check

        if DataLetter.isupper(): # == "Specs":
            FileToBeEdited = "Specifications.txt"
        else:
            FileToBeEdited = "DataSpecifications.txt"
        
        with open(FileToBeEdited, 'r') as infile:
             for lineEQN in infile: # loop to find each line in the file for
that dose        
               if ((lineEQN[1:2]== DataLetter)):
                   A = lineEQN[1:46]            # Whole Line
                   a = lineEQN[34:46].strip()   # Just the Data
   #     print("A = " + A )
   #     print("a = " + a)
          
        return(A, a) #Return the line and Data separately
    
    #===============================================================
    def ClickSubmit():
        window.destroy()
    #===============================================================

    label = ttk.Label(window, text = "Enter the new readings")
    label.grid(column = 1, row = 1)
     
    ThisList = FillTheList()
    x = 3  # Allows for two rows at the top of the form used for headers
    y = 0  # Scans the datafile to fill the list

    New_Specs = []
    #SpecsToUpdate = []
    
    for lineItem in range(len(ThisList)):
    
         SpecLine, Spec = GetLineByItem(ThisList[y])
         OldSpec = Spec
         NewSpec = " "

         SVRlabel = ttk.Label(window, text = SpecLine + "  "*5)
         SVRlabel.grid(column = 1, row = x,  sticky=tk.W)
                    
         NewSpec = tk.StringVar()
         New_Specs.append(NewSpec)
         SVRCodeEntered = ttk.Entry(window, width = 15, textvariable =
NewSpec)
         
         SVRCodeEntered.grid(column = 2, row = x, pady = 15, sticky=tk.W)
         SVRCodeEntered.insert(0, OldSpec)
         x += 1 
         y += 1    

    #===============================================================
    button = ttk.Button(window, text = "Submit", command = ClickSubmit)
    button.grid(column= 2, row = 15)
    window.mainloop()  
#===============================================================

EditDataByForm()
print ("Done")
#  Code needed to pull the updated fields from the form
#  as variables or in a list/array.  Once I have that, the code to replace 
#  code in the specifications.txt file has already been written.

#  Here is a sample of the Specifications.txt file:
----------------------------------------------------------------------------
---------------------------------------
-E MSN Monitor Serial Number       JNGY263-T4464                    ##   
 -
-F TSL TestStrip Lot Number        45001 82990                      ##   
-G SED Strip Expire Date           2021-05-31                       ##   
 -
-H SSC Sensor Sequence Code        71                               ##   
-I SCN Sensor Code Number          G03                              ##   
-J SSN Sensor Serial Number        2021-01-31                       ##   
-K SDE Sensor Date to Expire       2021-01-31                       ##   
-L SDN Sensor Day Number           12                                ##   
-M FDS First Date for Sensor       Fri Aug 17, 2020 09:34           ##
 -
-N IDT Insulin Dose Total          450                              ##

----------------------------------------------------------------------------
----------------------------
Footnote:
Some mornings it just isn't worth chewing through the leather straps.