I did similar, although the tool I made up to turn the lens carrier (made out of an old knife blade), had to be ground concave in the middle - to avoid scraping the convex objective lens!
That was a model M8 6X42. Other Leupolds may have the front lens set deeper in the objective bell?
I fixed the above tool in a vice, held the scope tight, and leaned into it with all my weight to avoid the scope slipping against the tool.
It was so tight that there must have been some kind of Loctite used during assembly. Some might say a bit of heat might make the job easier - but there's no way I'd use heat on a scope.
Once the carrier was moved with the tool, it was easy to fine-tune the PX distance turning the carrier by hand thereafter, and fix it in position by screwing on the end cap, hand-tight.
It's not a job I'd want to do again.