These weren't designed to be repairable. Apparently Zenith expected to sell you a whole new tone module if you broke one of the plastic tabs. The pivot rod appears to be held down by staking of the pot metal channel lugs that the rod sits in, at each end of the rod. You can probably grind off the staked-over material with a Dremel tool carbide bit, then pry out the rod with a skinny steel tool like an awl. When you reassemble it you will need to glue the rod in place with a few dabs of heavy epoxy like J-B Weld.
Depending on the module type you may also have to remove a staked-down latch plate to get to one end of the rod, and that will have to be epoxied back in place, too.