Arbitrum eath

Please help.

I transfered some eth from Binance to the coinbase wallet, because I wanted to use them for a NFT on Opensea. I used the Arbitrum network because it was cheaper. That was probably a mistake since OPensea do not support the use of Arbitrum Eth. My problem is I don't kow hos to convert them to the main chain. How do I do that? Also is it possible to send the eth to metamask? Or do i need to convert them somehow before?

Thanks in advance.