Admin login problems

Hi,

I'm trying to get into a very old iMac, which we haven't used for maybe 5 years.

We don't have any other Apple products.

I know my Apple ID but don't know my old login password. When I try to get in, after several failed attempts, it doesn't prompt me to reset using my Apple ID.

I also don't have an Apple keyboard so don't have a 'Command' butting to press with 'R' to perform a reset.

I can get into a linked account on the iMac but that account doesn't have any Admin rights so I can't get in that way.

Does anyone have any suggestions??