This is a mechanical issue, so you posted correctly.
Buy new bolts and retainers for the straps. Two of them. Replace them without question. Straps, too, if yours are rusty. These are inexpensive. You will also need a new tank seal.
Get as much gas out by running it low, or as low as you can. Back the car up on ramps. Disconnect the return and supply lines, as well as the filler neck and vent.
Move your ebrake cable if necessary.
Drop the straps and tank, disconnect the pump/sender, and let the tank down on a creeper. Pull it out. Two people makes this easier.
Unlock the retainer by twisting counter-clockwise. CLEAN UP THE SURFACE WITH COMPRESSED AIR or air in a can (duster aerosol) before the retainer ring comes out, and after. You don't want that crud in your tank.
You should be fine from there.