There are a few ways to resolve this dent issue.
glue these plastic ding tabs to the gas tank. You can find them by googling "plastic ding tab"
You will use a hot glue gun and hot glue them to your gas tank.
Use a dent puller slide hammer. The tip should screw into the plastic ding pullers.
Pull the weight of the slide hammer to the bottom towards the gas tank and give it a good pull. When the sliding weight hits the stop at the end of the hammer the transferred energy will pull onto the glued tab and pull the dent out.
You may need to repeat the operation a few times to get the way it needs to be.
This isn't very elegant but I have used compressed air by sealing the top of the gastank, removing the petcock and blocking off any cracks. I use one of the two screw holes for the petcock to insert a rubber tipped air gun and charge the gas tank up.
It CAN ruin the tank if you over fill with air pressure. You can set the regulator on the compressor to only give you 30psi to start and work your way up in 5psi increments until the dent pops.