Add Device
When you try to use Remote Play and it becomes necessary to register your device, a guide explaining device registration appears on the connected device. Select (Settings) > [Remote Play Connection Settings] > [Add Device] on the PS4™ system, and on the connected device, enter the code that appears on the PS4™ system.
For details on Remote Play, visit the PS Remote Play website.
https://remoteplay.dl.playstation.net/remoteplay/