Hello, since you do have not the know and the tools to solve the button if it is out of service, I will give you some advice to possibly make it work again. Already disassemble the console to check the status of the button it must resemble to the button for the L and R keys, the metal part can have move/ no longer be present on the button if it is no longer present the buttons that cause the pieces to power the console must also move in the console, Putting them back in place is quite complicated but feasible with a little patience. If this is not the case you can try to clean the button with alcohol at 90° without pressing the button too much, if you see the button moving while you clean it then it is desoldering, so stop.
If none of these solutions works any real repair store that knows how to repair game console, can repair it in no time and for a good price