i believe you'll have to uninstall knots, download bitcoin core, and wait for the download of the blockchain again. Once your bitcoin core is synced to the latest block, it should work with your existing lightning nodes.

I did this but in reverse: I deleted bitcoin core, downloaded knots and once it had synced it worked with both my LND and CLN nodes no problem (I use start9 too).

As for your photo, this error is occurring because you currently have knots installed, so that bitcoin core update won't work ( I too have that update appearing on my server dashboard every time I log in. Must be a bug).