I am desperate, I don't know where else to look. I have this score where I need to turn 3 sixteenths into a triplet. Is there a way to select the three notes and make them into a triplet? I really need to do it this way because if I delete 2 notes and then make a triplet out of the first one with the usual way, then it will make the triplet, but not calculate the correct metric value of the triplet, leaving an unnecessary sixteenth rest. At least a way to delete that damn unnecessary rest would be something.
There shouldn't be any way to make three sixteenth notes into a triplet, since they can be written normally. Tuplets, in general, are used when composers want to write a division of the beat that cannot be expressed in powers of two.
For example, you could make four sixteenth notes into a triplet, and the three notes played would be played in the same time duration as four normal sixteenth notes. The notation means to play three notes in the same time it usually takes to play 4 notes. (If you did this, there would be no extra rest, since all 4 notes would be included within the span of the triplet.)
But you're suggesting using a tuplet to tell a performer to play three notes in the time it usually takes to play three notes. Do you see the redundancy there? You've written a three-against-three polyrhythm. No one would enjoy reading that mangled tuplet notation (in fact, perhaps Musescore automatically realises this and doesn't allow you to do that), because you could just write all three notes individually, making it much more legible.
Tuplets can signify things like 4:3 (four notes in the space of three), and your basic triplet is 3:1 (three notes where one would be). Three notes in the space of three is just regular notation; don't make it any more complicated than it has to be.