Just hover over the region and click Edit (4). If you want to quantize all notes in a region, there is an even quicker way of doing it without opening the Piano roll. If you're unsure which subdivision to choose, 1/8 or 1/16 will work in most cases! Right-click and select Quantize and choose your desired subdivision (3). Select the notes you want to quantize, either by clicking and dragging a selection, or click once anywhere in the Piano roll and press Cmd/Ctrl+A if you want to select all of them (2). The Piano roll will pop up and show all the midi notes.
Hover over a region on a Soundtrap instrument track and click on Piano roll to open it (1). The Piano roll allows you to see what happens when you quantize, so let's start there! You can choose to quantize your recording either in the region Edit menu, or in the Piano roll. Have you recorded a software instrument that turned out a bit too sloppy timing wise? Try quantizing! When you quantize notes, they will end up on the beat instead of in between beats.
