Where to ask basic question re: restricting subforum access

[celux]

Hi people + thank you for the forum,

If this isn't the right sub-forum for this query can a mod move it please, our 1st post so go easy

Basic question: how do we learn how to restrict member access to a certain sub-forum (which is actually the sales forum) on our little site?

It used to be pretty easy when we were on phpBB and we still have access to the old forum so we can see the 80 odd members who should have access enabled.

We want to restrict access to members with 30 days membership + 25 posts.

Running vBulletin? Version 5.4.2

Thank you in advance.