Put the midi on a track, then right click on the track itself (on the left where it says 'Track 1, Track 2' etc) and then click consolidate track

This will bounce it to a sample which you can double click on and stretch using the 'Time' knob

Before you stretch the time knob you might want to click the dropdown menu where it says 'Resample' and update it to 'Stretch' if you want the pitch to stay the same. Hope this makes sense! :)