Hi Toril, yes this is quite easy and I am sure someone will post detailed instructions and probably a video link.
But essentially, open Recording, choose MIDI multi recording. Then touch the "New Song" label and find your previously recorded MIDI.
First note : You need to use a free (empty) track. Which track is free depends on what you did in your quick record. Parts R1, L, R2 and R3 default to record to tracks 1, 2, 3 and 4 respectively. Multipads 1, 2, 3 and 4 record to tracks 5, 6, 7 and 8 respectively. The style records to 9-16. If you used all 4 parts, all 4 multipads and the style - well then you are out of luck, because there's nowhere left to go

Second note - Touch the icon for that track, which opens a window to select which part it's going to 'listen' to. Make sure it's set to "listen" to part R1 otherwise your playing will not be recorded. This is probably the step that most people get wrong at first. After selecting the part, the track will automatically "arm" for recording.
Third note - Based on the second note, if you've only armed one track, and set it to listen to R1, then anything you play with L, R2, R3 or a multipad will not be recorded. But you can arm more than one track at once, each one set to listen to a specific part.