Adjusting convergence

[lnx64]

Ok so my 20" RCA ATSC TV has been good to me so far. I have cable on it via YPrPb inputs, and it looks fantastic, but I'd like to dial in the convergence on it. It's this set: https://imgur.com/a/vEHqTOB

There are no magnets stickied to the CRT whatsoever, and I saw in my grandmothers nursing home, the same model as mine, and the convergence is amazingly perfect, so I'm almost fairly certain I can dial this in even further.

Is this all done by the rings on the neck of the CRT? Or would this require magnets? I have already rotated the yoke to fix a rotation issue it had, so it's straightened perfectly now.

Service menu has nothing for convergence, only simple geometry stuff (including a very poor pincussion setting, which only adjusts the bottom half and not the top).

If not it's fine either way. This is just a bedroom TV.