How to record a ringtone in recording studio?

I wouldn't record ringtones at a studio. Record music at a studio then you can cut it down on your own and make a ringtone. I personally use garageband. I take a song, and import it, cut it down to the size I want and then export it. From there I can use bluetooth from my laptop to my phone and put it on the phone.

All you need is a music editing software and bluetooth (or a way to send the file to your phone).

If you really want to do it at a studio, you can just record what you want the file to be, then you can get a file the size of the ringtone from them, and you would probably still be responsible for getting it onto your phone yourself. If you have to record something, I would suggest a cheap USB mic and a downloaded copy of audacity and you can record and edit something.