First you need to determine what type of bend you have. The spoke tension will need to be more even than it is now in order to do so. Probably a good idea to release most of the tension to make sure the rim is actually bent, rather than temporarily distorted.
If the bend is U shaped then you need to just bend the middle while pulling or supporting the two sides. As you see above, there are a variety of approaches, from slam it on the floor, to push with your knee and pull with the hands, to using a doorway or levering it.
If it is an S shape (sharp right then left, and gradual return to the right) then you would need to place it in some sort of gap and carefully twist in the opposite directions - MUCH harder to correct.