There is no menu option to set iteration. You can only increment it by doing a check out/check in.
The bigger question is WHY?
What does having the same iteration do for you?
If you study PTC training documentation you will see that revision.iteration 4.4 is the same as 5.1 after doing a revise to the file. Only when you get to 5.2 is the file different than 4.4.