Use a spudger to gently pry the battery connector straight up from its socket on the motherboard. This will keep the Joy-Con from powering on during the repair.

Be very careful as you pry up the connector—if it doesn't come up with the spudger, try gently pulling the cables straight up from the board to disconnect it.

During reassembly, press the connector straight down into its socket on the board to reconnect the battery.