Hello as you have not stated which controller you have ( as post #2 ), I can only give you general advice.
Search this Forum and you will find step by step instructions on how to open the controller, make sure you have the correct tools.
1). Once you have the controller open the first thing to do is unplug the battery from the PCB board.
2). Look at the connector on the battery to see if there is any trace of juice on the connector, if there is use a tooth brush and warm fresh water to gently clean away
any contamination, DO Not wet the battery.
3). remove the circuit board from the controller, and using a soft brush, "like a make brush " use warm fresh water to gently clean away any juice residue.
4).unless you know what you are doing do not use a hair dryer or other heat source to dry the circuit board, if you have a can of compressed air ( you can get this from a camera shop ) to blow away the excess water, pat the circuit board dry with a soft cloth, and then put the circuit board in a container and cover it with uncooked rice, this will help draw the moisture form the PCB. Leave the PCB in the rice for 24 hours, after that time give it another blow with compressed air to get rid of any rice grains etc that might be stuck.
5). before reassembling the controller completely, make sure the antennas are connected, and any other switches are all plugged in, then reconnect the battery and turn it On, if you act quickly and you are lucky the controller should be OK.
Good Luck
Waylander