I'm new here, so sorry for the newbies questions

I have a situation in my flat that I am renting out to tenants. I remembered I fitted a cheap mechanical lock on of the bedroom doors but I do not remember the code and after 4 years of renting out the flat... they closed the door locked and cannot open it again.
They are about to call a professional and will charge around 250 GBP for the job; needless to say I am motivated to find a solution...
I could not find online the exact type of lock it is but it is of the cheapest of the cheapest, 10 buttons only, 1 to 9, and a C button.
Any thoughts?
Many many thanks in advance!
Cheers!
Alex