You need a lot of information to do a patch. Once you know what fixtures you have and their addresses the actual patching is pretty straightforward.
If the desk was patched before then someone must have done it. They may have a showfile. If not they must have had the information you need. They should be able to help - are you able to contact them?
Failing that. What is your situation? Is this a school, a community theatre, etc? Is there a tech responsible for it, other users, etc, who may have showfiles? They may even be on this forum but not realise it's "their" venue.
Where are you? Another forum member may be close by - it would help avoid us asking lots of questions if someone experienced could take a look in person.