If purchased directly from Apple, in most regions/countries, you have 14-days within which an unwanted undamaged device can be unconditionally returned for exchange or refund. Beyond 14-days, this opportunity is lost.
If not purchased directly from Apple, you will need to investigate the returns policy for the retailer from which the device was purchased.
As for trade-in, Apple does not accept “current” models for their trade-in programme. Consider also that trade-in values are always considerably less than the retail price that will have been paid at time of purchase.
If you are unable to return the unwanted iPad to the retailer, you would be best advised to sell your iPad privately - accepting that you’ll need to offer an appreciably lower price than the buyer would themselves purchase a new/unopened device.