my Bluetooth after forget headphone can't connect anymore

Hi ElvisTan,

Thanks for posting in Apple Support Communities. It looks like you are trying to connect headphones. Right? First, try connecting another Bluetooth device. That will narrow down whether this issue is isolated to the headphones or your Mac. Next, use the following guidance from If a Bluetooth headset doesn’t work with Mac - Apple Support which can help further.

• Make sure the headset is turned on and in range.

• Make sure the headset is connected with your Mac. Choose Apple menu  > System Settings, then click Bluetooth  in the sidebar. (You may need to scroll down.) Check to see if your headset is in the list of devices on the right.

If your headset isn’t in the list, try connecting with it again. See the documentation that came with your headset for information about connecting your headset with your Mac.

• Make sure the headset is charged or has fresh batteries.

• Make sure the headset is selected as the input or output device in Sound settings. See Change Sound settings on Mac.

Take care.