The two clubs established a partnership last season. Nash will work inside the GAIS academy.
He will work closely with academy director Sebastian Lindström and focus on player development and transitions from academy to the senior squad.
"It is very good for us to be able to have this exchange of experience, and an opportunity for our coaches and players to get feedback from a person with strong credentials in youth football in England and in Ireland," said Magnus Sköldmark, GAIS' technical director.
"This project will also mean that later this autumn we will have the opportunity to put together a team with young players from our academy and go over to Great Britain to meet other academy teams. It's not completely nailed down which clubs it will be, but it could probably be some famous teams."
Nash also said: "As an Irishman who went and lived abroad as a youngster, I appreciate seeing different cultures and watching football in different parts of the world. I appreciate what it can teach me and help me grow as a coach. I think it was just a unique opportunity for myself to come and experience the really high level that the guys are at now and get to see the academy up close and really look at player development in Sweden. It was just a really interesting and exciting opportunity and I'm really glad it's happening.
"I will come in and have a real focus on player development to help the club in any way I can. It is in player development that I have my background, what I have as experience from in my previous roles in the UK.
"I am happy to help any player in any way I can, with my experience. I spent a lot of time in my previous roles looking at trying to develop players for an A squad, and improving players that are in and around that environment. That's where I really want to come in and help."