Connect the phone to a PC. If it shows as QHSUSB_BULK or Qualcomm HS-USB QDLoader 9008 , it is in emergency mode.
Once the emergency payload is accepted (often indicated by a red flashing screen), you can flash the full FFU image to restore the phone to working order. Note for Spec B Devices: The lumia 650 emergency files new
Since Microsoft has largely discontinued support, the community has archived these files on third-party platforms. Connect the phone to a PC