Can I return a MacBook Air after formatting it?

If its been less than 14 days since purchase from Apple or an Apple Authorized reseller, yes, you can return it to Apple.

click here ➜ Returns & Refunds - Shopping Help - Apple

To clarify the above, if you purchased it directly from Apple, you can return it to Apple within 14 days.

if you purchased it from an authorized retailer, contact the retailer you bought it from. For clarification of their return policy.