Agree with 'best do nothing' approach but with the proviso that the dent has not affected the wheel angle in the frame.
A google on checking frame alignment will give some simple tests to assess alignment issues that just an eyeball
of whether the wheel sits straight in the frame will tell you. In the event the tube cracks at some point what would
be the effect? probably the wheel would shift into the frame and you would slow down rapidly, so riding at <25 mph
or so and wattage outputs under 250 would be prudent. That is if you were sprinting and it cracked you would crash,
but just tooling along you would stop and maybe fall over.