How to return the device on MacBook Air on Bluetooth?
Make sure to be more clear next time. We can't really figure out what you mean by 'I tried everything' ;)
On your Mac :

Go to Apple () menu &gt; System Preferences &gt; Bluetooth


On your headphones :

Press the power button for 5 seconds
Wait for the led to flash
Go back to your Mac's bluetooth settings, at the bottom of the devices list you should now see a Connect button next to the headphones icon / name (as shown on the example below)


Source: https://support.apple.com/en-us/HT207108