Welcome to the forums.
At the end of each week, you need to either:
1.Make a new copy of the spreadsheet and input your new maxes (if you like to be able to maintain a training history, which can be helpful - I do this and put the date in each file name so I know when it was)
2. Overwrite the TM formula.
In the spreadsheet, it says “You will have to manually enter your new Training Max, which will overwrite the formula (that is okay!)”