Likely flaps/slats were set when the takeoff configuration warning horn probably sounded as the thrust levers were set for TO thrust.
That is probably how it has been handled many times in the 'old days' here in the U.S. Often the takeoff checklist itself was completed on the roll by 80 knots.
However in these enlightened times with FOQA, FDM, ASAP and all the rest you are probably better off to do a low speed reject, find out for sure why the horn went off, put it in the logbook or not depending on the carrier and try it again after being sure you don't need a sign off. And do a
mea culpa with all crewmembers on ASAP and NASA reports to CYA.
Moving the flap lever on the takeoff roll on a modern plane causes all heck to break loose with the warnings as these guys at Charlie West found out:
Pilots Engaged in Small Talk Before Jet Botched Takeoff - WSJ.com
The Captain moved the flap lever from flaps 8 to flaps 20 on the takeoff roll and botched a reject over V1, but was saved by the crunchy EMAS at the end of the mountaintop runway.