In a measure that had a set of triplets, 2 had brackets and 1 did not. (See Capture_01) After selecting the bracketed “3”, I changed it to non bracketed but the "3"s moved distinctly away from the notes. (See Capture_02) I then selected the middle “3” and (in Engrave mode) pressed Alt-Up Arrrow which caused the “3” to move down. (See Capture _03) A repeat of Alt-Up Arrow moved it down even more. Trying to move the “3” with the mouse was disastrous.
I had to use the lower panel properties to move rests up/down, maybe it will work with tuplet numbers as well.