I assume it is the end prong and you are in the UK.
Go to the nearest grid and lift it up, insert the prong into the trellis of the open grid and bend it back by levering the handle!
This is easier than bending it out of alignment as you are only putting pressure on one prong.
If you look around there are many suitable "fixed points" you could use for this, maybe try the gatepost or a concrete fence post....... but don't forget to drop the grid back after you have finished!