by loosening the two bolts on the opposite side of the bar and tightening the bolt on the top side you might get the problem bolt untensioned enough to use radio pliers to slowly extract
or, you could use a screw extractor
or, you could epoxy in an allen key
the last two will also benefit from untensioning the bolt slightly from the first option
by loosening the two bolts on the opposite side of the bar and tightening the bolt on the top side you might get the problem bolt untensioned enough to use radio pliers to slowly extract
or, you could use a screw extractor
or, you could epoxy in an allen key
the last two will also benefit from untensioning the bolt slightly from the first option