Linked records to a particular user/user group

I’m setting up a Client Portal for my Sub-Agencies.
Each of them will only access a list of Students, Applications linked to that particular agency.
I want to know how to configure a particular user (linked to a particular agency in Agencies table) so that user can only access, see, edit and create records for that agency only, and cannot see records of other agencies.
I’ve setup user groups for: Admins, Agencies in general, but don’t know how to link details to one agency.
Please help me. Thank you.

This can achieved by conditional filtering what you have to do is link each student to the agency they belong and then filter the record as loggedin user email is connected agency email