If you can tighten the bolts, do so as it will ex span the nutsert tighter in the hole and maybe reseat it. Either way, heat and lube the nutsert through a frame hole.
When it still spun, Ive used a prybar or apply force between the frame and bracket to pull the nutsert down with more force than what it wants to spin. It takes a few times and even a hammer to wedge it, but it has worked many times for me. Once out, tact weld them or replace with new nuts (and weld those)
1975 CJ-6 1983 CJ-8
1986 CJ-7 Laredo 1986 TJ-7 Trail Jeep
2003 Inca Gold TJ Rubicon