Locked device and cannot remember password

I recently upgrade my phone and took my SIM card out of my Samsung Galaxy S6 and replaced it with my sons. Having forgotten that I had Anti theft turned on on that device. Subsequently the phone has been locked. I am unable to remeber the passcode.

Anybody have any ideas?

Many thanks in advance

Adam

https://support.avast.com/article/127/ (Restore forgotten PIN)

after removing the card from the phone Avast locked the phone in airplane mode and I can not connect to the network to reset.

I wouldn’t have a quick and simple solution, but have you tried going into a local mobile-store?