It is good to keep in mind that actually there is no lesson field in this form. The lesson is only printed to distinguish between assignments when there is more than one item of the same type. (If you were handwriting them, you could use something else to make the distinction)
I wonder if the lesson # appears in the main screen of TB?! It looks like the lesson numbers are not imported at all. If not:
Unzip attachment. In TB | Settings go to the >_ sign in the bottom RH corner. Navigate to the unzipped txt file and execute. Reimport the workbook.
1. Download S-89 as pdf from jw org (log in first)
2. Define a custom template folder in TheocBase - Settings, if you have not done so already. See picture ('My Documents' is not a good example, but it is just an example). Attention: At least inWindows the default C:\Program Files\TheocBase\template folder has restricted 'write' permissions. So you cannot use that folder (unless you change the permissions.)
3. Put the S-89 (pdf) into that custom template folder (defined in 2)
4. Open Theocbase and go to print. Theocbase will now do a conversion.