Hi any1 know how to save the current tuned FM frequency into any 6 preset on the multimedia system?

I have read thru the user manual, but the user manual did not mention on how to save the radio station. So after I tuned to the favorite radio station frequency, what i needed to touch on the LCD screen or press on the physical button in order to save the radio station to the any 6 preset displayed at the left side on the LCD screen?

thank u