To switch between Bluetooth and FM radio modes on the MUZEN OTR Metal Portable FM Radio Bluetooth Speaker, you can use the knob located on the top of the speaker. Simply turn the knob to the left or right to change modes. When in Bluetooth mode, the speaker will automatically connect to the last device used. To search for FM radio stations, tune the dial to your preferred frequency range. The speaker will then pick up FM radio stations based on your location.