Kal Ico wrote

I have a small air compressor and one of the fittings
to the air tank has sheared off. You can see it he

https://photos.app.goo.gl/w44v8jSG2noBKVHv5

https://photos.app.goo.gl/xAaN8WTswVh6wuCQ6

Can anyone recommend the best way to get the old bit out

An extractor should get it out.

and suggest how to repair/re-thread so I can use it again?

A tap should repair it fine.