Gosh....I don't think you need to remove the lower unit to remove and replace the trim tab. On my 1968 50 HP mercury there is a hole that is covered with a plug directly above the center of the trim tab. I have to use a extension with a socket to reach about 4" to get to the bolt holding the tab. Now your tab looks to be bent out of place but you might try and mark the former location of the tab "fin" to reinstall in original orientation. In that way you can keep the boat tracking in the correct direction without having to adjust multiple times to find that original sweet spot.
Greg
Wisconsin