Nintendo Switch Manual page 24

You can pair the Joy-Con controllers to the
console by attaching them once. Then you will be
able to use them while detached from the console.
Up to 10 Joy-Con controllers can be paired to
each console at a given time.
Detaching the Joy-Con controllers from the
console
Detach the Joy-Con controllers from the console to
play Nintendo Switch in TV mode or tabletop
mode.
To detach a Joy-Con, hold the release button on
the back of the controller, then slide it up.
Hold