How do I delete one item from Apple bag on MacBook Air?

By "Apple bag" are you referring to making purchases at the online Apple Store? If so, did you actually make the purchase or planning on doing so after correcting the items in the bag?

If you haven't made the purchase yet, try the following:

1. Go to the Apple Store online: https://www.apple.com/store.
2. Click on the Bag icon in the top right corner.
3. Find the item you want to remove.
4. Click the Remove (X) button or Edit next to the item.
5. If prompted, confirm the removal.

This should update your Apple Bag, and you can proceed with your purchase without that item.