Tuplet question: 13 in the space of a dotted quarter in 6/8 time

Assuming you want a sixteenth note tuplet, enter a dotted quarter note or rest, select it, go up Notes > Tuplets > Other..., and enter that you want 13 notes in the space of 6.

It takes some getting used to, but it's not that hard once you've got the hang of it.

1. Make sure you have a dotted quarter rest (5.)
2. Go to Notes > Tuplets > Other…
3. Change the relation field to 13/3 as you want to fit 13 notes where otherwise 3 notes would've gone (so 13 eights instead of 3)
4. Press OK

Now you'll have 13 eights instead of 3.

If you'd change the relation to read 13/6 you'll get 13 notes in the same dotted quarter, but now as 16ths, because there fit 6 16ths into one dotted quarter.

[EDIT] Likewise, a relation of 13/12 gives you 32nd notes.