The Elemental Adept feat says that I can treat any 1 on the damage dice as a 2. Does that meant that, if I've chosen fire, when casting the Fire Bolt cantrip I can roll 2d20 instead of 1d10?
It doesn't change what dice you roll, it changes how you read the dice. When you roll, any dice that come up showing 1 you treat as if they had rolled a 2.
So if you roll 1d10 and get a 5, Elemental Adept doesn't do anything; but if you roll 1d10 and get a 1, then you treat it as a 2 instead.
It's not so useful on a 1d10 because it only does anything 1/10th the time, but it's much more useful on 3d6 and other rolls that have multiple small dice.