There are three holes for springs, but in multiple Pebble Time Rounds that I've repaired, I've only been able to recover two springs. I'm either bad at keeping track of them, or some models are manufactured with 2 springs. The reassembled watches seem to work fine with only two springs. I recommend one spring on the right and left side.

Use tweezers to gently place a spring in each hole, being extremely careful to not lose them.