Use the tip of a pen or paper clip if need be. You do not need to hold the button down; it will activate after a quick push.

If the LED lights on the Wii remote have stopped blinking, just push the SYNC button one more time. When the player LED blinking stops, the process is complete. You’ll see an LED illuminated on your remote, indicating that remote’s player number. This procedure must be repeated for each remote you’d like synced up.

One-Time Mode synchronization lets you use your remote on a different Wii console (say a friend’s) or a different remote on your console. You can also use it to change the order of players without turning off the Wii and starting over. This does not get rid of the settings in Standard Mode. Once you turn the power off, the settings used in One-Time Mode will go away, never to return. If you accidentally turn the power off, you will have to start the process all over again, as your Standard settings have taken effect. [1] X Research source

Make sure both the console and the remote are on and working.

It’s only temporary. If you’re syncing to someone else’s console, your remote will unsync when the power is turned off.

The Player LED will blink during the syncing process. When the blinking stops, the connection is complete. If you are syncing multiple Wii Remotes, press the 1 and 2 Buttons on the Wii Remote you want to be player 1. Immediately after (without a significant pause), press the 1 and 2 buttons on the remote you want to be player 2. The order in which you push the buttons determines the order of the players in multiplayer games.