How to change CID Num

Hi,
I have 2 internal phones used in a training location.

Instructor need to dial the other phone with 3 different CID Num’s, acting like the phone call is coming from 3 different locations.

I was thinking if the instructor dialed:
Ext#:500 it would be forwarded to ext#:900 with CID from ext#:500
Ext#:600 it would be forwarded to ext#:900 with CID from ext#:600
Ext#:700 it would be forwarded to ext#:900 with CID from ext#:700

New to FreePBX.

Out of ideas here, can’t make this work, any tips in the right direction is higly appreciated.