Hi Rick, and welcome.
If my memory serves me right, your 883 Iron came stock with the low suspension. If lowered further, you really should get it back to stock height. You might get away with reducing the preload on the shocks, thus raising the bike slightly. There should be five positions available and the wrench is clipped under the front of the seat.
You might also want to verify the rear tire is the stock size. Too tall a tire could be the cause of the seat mounting bolt striking the tire, or even a too long bolt. Tire size should be 150/80B-16, either Dunlop or Michelin stock.
Eventually you might look at Progressive Suspension rear shocks and front springs. Progressive 412 work well and unless yours has the cartridge system in the forks (don't know when Harley started using that, my 2016 Sporty came with it), their progressively wound springs work well. There is enough vibration in the Sportster line already.
Also, pick up the Parts and Accessory catalog from the dealer's parts area.