I'm assuming it's one of the programmed keys with a battery.
Carefully open the remote, remove the battery and dry the unit thoroughly before reassembling. (Think same way you'd dry out a cell phone you dropped in the water.)
While it's drying check the battery to see if it has any voltage. If not, replace it.
Hopefully all is good.
If not, it likley has lost it's programming or damaged the chip(s) and you need to visit a dealer or a locksmith. Hopefully they can just reprogram it and it won't cost a lot.
Welcome to the Rider Forums first. Second, if this is about a Concours 14, does the bike start with the RF key? Check the owner's manual for how to use this key. If the bike starts, the situation starts to indicate there is a real problem with the larger key fob. Then, do as @Obo tells; and, while the fob is opened up, be sure it is dry inside. Lastly, put that key fob on a lanyard. Loop it through the belt and into the pocket. This way, it won't get dropped and lost; and, not likely to get put through the wash machine. No help if he jumps into a lake at a stop.