I have an iPhone 5 that is disabled. It is not recognised in iTunes/Music. I can prove it is mine. Can anyone advise - please?

I found an old ipHone in my drawer that I think is an iHone 5.

It is disabled as we have all tried to guess the passcode. I can't 'see' the device on iTunes or Music probably because I have a new iMac.

I am sure that I can ultimately prove that I am the owner as it was either on an O2 contract or purchase from Apple (I think the former).

Please would anyone have any advice on how I might be able to get the device unlocked?

Thanks