Fab four rear bumper issues

I bought a fab four bumper after the spouse backed into my truck. My son installed it and was on for like 3 years when the spouse noticed that it was crooked. Like a good half inch difference. So I took it to the place where I bought my brush guard for them to "fix" it. However, the tailgate scrubs in the center. I 1st thought it was from a gravel being stuck btwn bumper and tailgate so I repaired the scratches only to find it messed up again. That's when I realized it was the bumper, not a rock. Can someone please tell me how to lower the bumper just enough for the tailgate to clear it?

 

I have a Fab Four bumper. It's most likely one or all of the 6 bolts that mount to the factory hitch plate underneath. The bumper probably wasn't aligned right while they were tightened.

 

I had problems with a fab four bumper over time as well I agree with the other reply that says it probably wasn't aligned properly before tightening the bolts.