Common sense should prevail.
Dress casual with a lean towards business-comfortable.
If that miffs your common sense then ask your mom or dad because you may not be mature enough to compete OTB.
Chess players are known to be hygeinically challenged - I think is a carry-over from Hikaru doing hours long speedruns or some such hostile version of chess, because, well, we all want to be like him (the smell is more easily achieved than the chess).