star trek - How did Odo give it to the founders in the Gamma quadrant?

The only problem with that was during the the occupation of Bajor (First Part of Season 5), the Female Founder could not get back to the Alpha Quadrant thanks to Rom's self-replicating mines.

I'd guess that it was all during Homefront. Odo was infected by Section 31 and Odo momentarily fused with the Admiral/SeaGull/Founder to expose that specific Founder. If Odo is Patient Zero, than the Admiral/SeaGull/Founder would be Patient One, not the Female Founder.