if you have DB Browser installed (see link below in signature), you can go to the database and open it. (if you do not know where to find it, in TB go to Settings, and click 'Open database location'. You'll see a file called theocbase.sqlite. Make sure to close TheocBase itself before making any changes, though!
In the second tab (Browse Data) chooose the table lmm_workbookregex from the dropdown. When in that table, filter for 'fon' in the language column. Make sure the input looks like in the picture attached.
What I think is that at this point maybe only the value after assignment1 is not correct. You can solve that by removing the filter, and copy and paste this value from any other 'assignment1' in the column. To be sure, choose it from French (fr), since you know that works. Make sure to save the database when closing.