Tuya Smart Energy plug. New firmware. Hardwire instead?

[deltamelter]

I have an ENER-J SHA5264 energy monitor/switch that has Tuyo firmware, apparently newer FW as the OTA method to does not work.
The device is easily opened with 3 screw outside and and 2 more inside holding the circuit board in place.
On the reverse of the board there are 5 relatively large, spaced solder points clearly labelled 5v, GND, RST, RX, TX and GPIO0
Are there instructions for flashing the tuyo devices with soldered connections?
Found a description of flashing one of these OTA, but that won't work, so looking to use the backdoor option...

[deltamelter]

reluctant to hook this up using 5v when all documentation suggestes 3.3v only.
Anybody got an insight?

[deltamelter]

sorted.