Sometimes we get a ring and has the bent or dented band... Some of us have a rounding mandrel... For me the best thing you can do is leave it alone..

IF it has a enamel front cartouche and bent band I'd say there's a very good chance if you try and get it perfect round with mandrel your going to damage the enamel. I've seen nice rings when band trying to be re rounded the enamel crack , even a piece come out... - It can be done without a mandrel but its something you need a bit of practice doing..

My newly acquired ring has a slight bend/flat spot [red]. The front piece [blue] is separate.. IF I try and re round it there is a very good chance the cartouche could come right off....

It's not a big deal. You wipe it down, admire it, get it in its case...