We used to do that a lot on bikes that came in for service, had a couple of sets of curved dollies, one set for 26/27" rims and one for 20" rims (not that we took much notice what size the rims were). Sometimes we wouldn't bother with them and held a big lump hammer against the good side of the rim before giving the bend a hefty tap* with a lighter hammer.
* Sometimes it was more of a clout than a tap.