B737-800 First Officer reported rejecting the takeoff at 35 kts due to a cabin door light. After positioning the door handle full down the light went out and the flight departed.

Narrative

Up until takeoff roll; no abnormal indications noted. Cleared for takeoff on Runway XXL; I was Pilot Flying. Around 35-40 kts.; master caution light illuminated; with a DOORS indication. Captain took the aircraft and performed abort; low speed; normal braking. The AFT ENTRY DOOR light was illuminated. I told Tower we aborted takeoff due to a door annunciation; and turned off the runway. Tower asked if we needed to return to gate or were planning to takeoff again; we said we needed a few minutes; but likely would take off. After parking; we spoke to cabin crew; Flight Attendant in aft said that the door handle showed slightly up. She made sure handle was pushed down; and our indications showed door was closed again. After rerunning checklists; we proceeded to takeoff again; with no further abnormalities noted.Possible failure to recheck aft door after catering came to aircraft; bumps in taxiway and runway may have jarred door handle loose.We felt that this highlights the importance of briefing each Flight Attendant about the need to check each door handle is fully down and closed.