Everyone should be able to roll their r's, but many people have a disconnect because they think it is done by moving their tongue and that misunderstanding prevents them from figuring it out.

It's done by cupping your tongue to the roof of your mouth and blowing air through the cup, the pressure builds up and then suddenly releases, and if done correctly it will vibrate and make a purring, rolling r sound.

The sides of your tongue abut your teeth on the sides and stay firm, but the tip only gets a little pressure to return to the roof of your mouth.