Alter the control (6)
I believe the answer is:
switch
I believe this clue is a double definition.
'alter' is the first definition.
(switching is a kind of altering)
'the control' is the second definition.
(switch is a kind of control)
(Other definitions for switch that I've seen before include "Cane to control the light" , "turn" , "electrical apparatus" , "Electrical control - change sides" , "Change; hair-piece" .)