[modern] Front Bumper on XJ40

Noticed the front bumper on my 1989 VDP off level at approximately 1/4".
Removed the front bumper and noticed the passenger side support (looking at
the front) missing a bolt and the other bolt very loose. The bolts on the
underside seems to be in place. The question I have is how do you tighten
or loosen the bolt? I tried to remove the remaining bolt to match a
replacement, but the bolt will not come off. I removed a little rubber cap
from the frame (next to the bumper support) and stuck my little finger in it
and I think I felt a nut at the end of the bolt. If that is true, do you
need a special tool to get to it? Would appreciate any assistance on this.