You can't do the return through Ebay.
You have 30 days to start a return and, if you can find the item in your purchases, it will state the date the return window closed.
You will have to communicate with the seller to get an address, and will probably need to purchase your own tracked label.
Be aware that if the seller doesn't confirm they have the item back (send it tracked) or refuses a refund once they do have it back, you won't be able to get any help from Ebay. This is entirely between you and the seller and will need a degree of trust on your side.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)