Note that this answer partially relies on personal experience, as my L1 is Italian.
Explaining the tongue position
When rolling the R, the tongue must be behind your incisors.
The biggest difference between the soft-R and the rolled-R is the source of where the r gets generated.
When doing a soft-R you generate the sound in your throat. When pronouncing a rolled-R, it gets generated by the movement of of your tongue against your upper cavity behind your incisors.
Other than that, I found that the best trick for actually making it work, is the following:
1. Use some ‘butter’
American and other English speakers may be surprised to hear that many of them can already produce a rolled ‘r’ sound!!
When you say the word “butter” quickly, the ‘tt’ sound is produced by flapping your tongue against the roof of your mouth, rather than a normal ‘t’ sound (like tree). USE THIS.
It may not be precisely the same as a rolled ‘r’ (depending on the language and dialect you are aiming for), but it is mountains more convincing than the English ‘r’ at the end of the same word is.
Try changing one letter at a time from ‘butter’ until you have your target word (e.g. caro) – use this sound and you’re work is pretty much done!
while this sounds different than a rolled-R, it's a good way to explain the tongue position.