A rolled R is a sound that occurs in many other languages, such as Spanish and Italian,...but in American English, a rolled R doesn't actually appear!
In fact, if you listen to American speaking other languages, a very common difficulty they have is trying to copy rolled R sounds.
Essentially, a rolled R involves some vibration of the tongue, whether the very back or very tip of the tongue, often against the teeth or gum. It can appear when an R is by itself ("air") in a word or when a consonant comes before it ("try").
However, what makes this sound impossible to attain in American English is that the placement in American English is so low. Rolling tongues typically require a placement that is higher, often in the mouth and towards the lips. American English, however, is projected from the chest/throat.
Play around with placements to try and remove a rolled R sound in American English; or, check this full video for more techniques: https://youtu.be/IJVlUxCQ1ek