Hello,
I run nextcloud in a shared webhosting environment and have no ssh access to the server.
Is there a way to trigger the conversion from php or SQL?
edit:
I just found the occweb app, but this seems to be not compatible with 17.0.2. It shows a warning.
Are there other ways to get the columns converted?
edit2:
I was brave and used occweb 
Worked like a charm. Warnings are gone.
Best,
Lars