Can't find the release for this wiring harness connector
Picture is a bit fuzzy to be certain, but typical for this sort of connector would be to slide a flat screwdriver up the center (between the ridges on the left part) to pry up a tab sticking down from the end of the slot on the right part. Or, to lift the end of the slot off a tab sticking UP from the left part.

Or, sometimes, the screwdriver goes in the slot, from the right. Picture is not clear enough to tell which flavor you have, either try it, or take a better/bigger/clearer picture.

They can be pretty stiff to get apart even when unlocked, depending how long they have been together and how tight everything is. You also need 3 hands sometimes, as the locking tab won't STAY out unless you can actually get the screwdriver under it, and sometimes there isn't room, without breaking the connector, so you need someone to pry and someone to pull at the same time.