Yes, you can use "Hard" way to force the display enter boot loader:
1) connect VCC, DATA and GND to a USB->UART adapter, the DATA pin connect with TX pin on the adapter, but don't plug it to computer (power off)
2) short the DATA pin to GND, and keep that.
3) plug the adapter to computer (power on)
4) reset the display by short the rectangle pad on the PCB to GND, and open the short.
5) open the DATA from GND
Now the display supposed enter bootloader.
6) run coolterm and config the adapter at 57600-8N1
7) transfer the firmware to DATA pin
If the display upgraded success, you can see Digole's welcome screen now, if not, please try above steps again.
The display was check the DATA pin when hard reset (not when power on), if DATA pin was low, then wait it go high and then enter boot loader. another way to enter bootloader is using "BLUBL}" command if the display still accept data.