OK, think I understand now. Here is how I would try to fix it. Get a good straight edge and some kind of jack. I would probably use a hydraulic bottle jack cause I have several, but a scissors jack or screw jack would probably work as well. Get the edge that has "sagged" top dead center. On the inside of the tank below the TDC edge put some shoring like 4x4 or 4x6 etc. to distribute to load and get the jack closer to the TDC edge. Put some more shoring in between the top of the jack and the TDC edge (like a short 4x4) again I think you want to distribute the load. Carefully jack a little at a time and use the straight edge to monitor progress. Bet you can get it back where it needs to be pretty quick.
Got a bunch of cooking toys and a custom metal fabrication shop where I spend my time building all sorts of smokers & outdoor cooking gear.