I’m trying to reset MacBook Air to factory settings
Purchased used MacBook air
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What condition was it supposed to have been in? If you expected a working computer, you should take it back for a refund.
If you need to star from scratch with this Mac: Use Disk Utility to erase an Intel-based Mac - Apple Support
Read the entire article as there're two approaches. Likely you need to erase the drive and install a fresh version of your chosen OS.
Did the referring article's instructions not work for you? That and the site I gave do the same thing, but you have to follow the guide precisely and skip nothing that applies to you.