Well, where did you import wave file? It has to go somewhere--either in a Voice or a Drum Voice as a Drum instrument. And MOTIF ES has an integrated sampling sequencer that can take that conga loop, slice it and generate MIDI notes that play it pack at the tempo of your song. You can even use loop remix to generate different variations.
If you JUST want to trigger a loop and have it play you would need to determine the tempo of the loop, place the sample into a drum kit on a note, open the pattern sequencer and just play the note every measure to trigger the loop. That's the oldschool way but there are cooler things you can do with an ES (like the stuff I mentioned up top).