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Hello there. It's pretty straight forward. If he already has a Hive account he can simply hop over to https://nftshowroom.com/ and he can log in with his Hive username.

After that he needs to go to his profile page at NFT Showcase, fill out the details and then clock the "Apply to be whitelisted" button at the bottom of the page.

They require that you submit a link (where it says website) to some web-page that shows some samples of your art. Also they you to have a Twitter account so they can verify who you are.

It usually takes a couple of days before they get back to you. They're a really nice team, and they're happy to help - you can chat to them on Discord (there's a link at NFT Showroom for this).

I'm pretty new to all this, but it's reasonably straight forward, and there's always friendly people who are ready to help.

Just let me know if you need any assistance :)

Thanks so much for the information really appreciate @mattbrown.art