Hello, I'm Chris. Welcome and thanks for asking your question!
I am unsure which connector you are having trouble with, is it the one below.
yes, that looks like it; tried to on lever tab in middle but it won't move.
This lever needs to move the full distance to the right to unlock. Often road grime gets in there and makes it hard to move. A shot of WD 40 around the connector and lock sometimes will help out. Also gentle tapping on the connector hitting it in the direction to seat it harder using a rubber hammer or the wooden handle of a hammer will help. Once the lever is all the way to the other side, wiggle the connector to walk it off.