How do I unpair my Bluetooth Headphones from my phone without access to my phone?

My problematic Allview P6 Qmax phone refuses to turn its screen on. Its touch screen has proven to still work, but it just simply refuses to open the screen. I bought a new phone, but my problem consists of the fact that my Panasonic RPBTD5K wireless headphones are still paired up through Bluetooth to the phone that won't show its screen anymore. I don't remember how to navigate to the Bluetooth screen in the settings with a black screen. I would like to know if it's possible to use... Maybe a third-party program, that's capable of unpairing my problematic phone from my headphones. Or if my headphones have a command to unpair from what they're paired with.