the kobo app doesn't recognize it, but does the MacBook show it as a mounted drive?
If so you can manually load a software update just find the one most recent for your Touch from:
https://wiki.mobileread.com/wiki/Kobo_Firmware_Releases make sure you grab the right one as there are more than one Touch 905.
You'll need to enable hidden folders to see the folder on the kobo to copy the update files to:
Open the folder where you want to search hidden files.
Press the Command + Shift + . (period) keys at the same time.
The hidden files will show up as translucent in the folder.
If you want to obscure the files again, press the same Command + Shift + . (period) combination.
You'll want to unzip the update file, and copy the contents of the resulting folder to the .kobo folder on the kobo drive.
If the Macbook doesn't mount the Kobo Touch the above will obviously not work.
The reason you are running into this issue is there was a change in wifi protocol support, unless your Touch was updated at the time of this change, its restore partition only carries the old now unsupported protocol.