Why i can’t make notifications when i left behind my iPhone?

I don’t quite understand your question. If you are asking how to have your Apple Watch notify you if you leave your iPhone behind, then please follow the instructions below. If this is not what you are asking, then come back and explain your question in more detail. We want to help if we can.

Set up Notify When Left Behind

1. On your iPhone, open the Find My app.
2. Tap Devices or Items.
3. Tap a device.
4. Under Notifications, tap Notify When Left Behind. If you don't see Notify When Left Behind, then that device might not be supported.
5. Turn Notify When Left Behind on or off.

Set up and use Notify When Left Behind in the Find My app - Apple Support