OP, little correction to your post - you probably have their debit card, because AFAIK Revolut aren't issuing credit cards.
And there is lot of options where you can buy Bitcoin using Revolut card - you can do it on any exchange which accept debit cards.
There's an option to buy Bitcoin directly in the Revolut app
https://www.revolut.com/exchange-cryptocurrencyJust you have to enable it in the dashboard (last tab).
Unfortunately I don't know anything else than that this option exists. No prices/fees, no info about the fees for withdrawal into a proper Bitcoin wallet...
You can't buy real Bitcoin and altcoins on Revolut and it's impossible to withdraw it. It works just like a sandbox