Puk it.
Do you have access to his phone details .... Network password etcm
If so, deliberately PUK it. In otherwords enter the first details wrong I til it says it's locked.
Then contact the network, and say it's blocked.
They'll give you an unlock code.
I know lots use a date of birth, or card pin, as their pin code.
.....
If I helped or solved your problem, please like or tick solved.
Have been using phones since 1993, and am self taught.
I offer advice for free, cos I think it'll help, if it doesn't, explain why, I might learn something new too.
Current phone Galaxy S22 Ultra
Previous phones: most S series, Note 2, Samsung Alpha, iPhone 3gs, far too many Nokia's!