Unfortunately, there is not a way to simply "transfer" your content over to Catapult from another distributor.
You would have to terminate your agreement with your other distributor, at which time (depending on your agreement with them) they would then issue take down notices for your content.
You could then submit this content again under your account at Catapult and we would deliver the content again to the music stores.*
*It's important that when you submit the album(s) at Catapult that you provide the same metadata (ie: ISRCs, Primary/Featuring Artists, Album Title, Track Order, Track Titles, etc.).