If the used iPad Air was not properly prepared for you a new user, you likely won't be able to perform what is required in order to use it. You MUST know the Apple ID and Apple ID Password which was used to set up the iPad. Do you know that?
If you do, this link will walk you through the steps you need to follow --> If you forgot your iPad passcode - Apple Support
If however, you don't know the Apple ID and Apple ID Password, it's a lost cause and you will not be able to reset the device. Apple will not help you, nor can we.
You'd need to get assistance from whoever you purchased it from. If you don't know them or can't reach the, the iPad will be ready for the recycle bin as it will be useless.
Read this as well --> The All Too Common SAD Reality of Buying … - Apple Community