Hello, my name is Pavel, and I will be supporting your case, there are two ways to do a mass erase, you could use the IDE with your debugger probe.
Look at the image use it at example, just need to know what kind of debugger you have.

The other way if you do not have the debugger maybe you could use the Uart and use the ISP mode on the MCU, then use the BLHOST to send a come for erase all memory.
Best regards,
Pavel