I’ve searched the manual. It seems like this should be easy.
Couple of ways…
a) drag each Part onto the same MIDI track, then click on it with the Glue tool until they are all glued into one Part.
b) Left and Right Locators around the desired start and end position, Solo the tracks, then MIDI menu>Merge MIDI in Loop.
Thanks vic_france! “b” was what I was looking for. I have files with drums separated on different tracks and it’s a pain to drag each manually.