I cannot get my MacBook Air to unmute

Refer to these instructions: If the internal speakers on your Mac aren't working - Apple Support. If you are attempting to de-select the Mute checkbox as described in Step 5 and it stubbornly remains selected, try resetting that Mac's NVRAM: Reset NVRAM or PRAM on your Mac - Apple Support.

"Settings that can be stored in NVRAM include sound volume, display resolution, ..."

This assumes your MacBook Air model has an Intel processor. If it is newer model with an M1 processor, that Support document is not applicable.

Identify your MacBook Air model - Apple Support

If the internal speakers on your Mac aren't working - Apple Support has a number of steps to follow, but if they are not working or don't make any sense, those instructions recommend contacting Apple Support:

Contact Apple Support