Sunwayman C25C Thrones - Problem with electronic switch - Please help.

Dear BLF community,

My beautiful Sunwayman C25C thrones is malfunctioning. It has turned into a momentary, tactical turbo flashlight (it lights up on full while I hold the switch).

I suspect the electronic switch is at fault, but I cannot be 100% certain. I have no formal electronics training and cannot analyse the circuit to find out what is causing it but I am quite able with the soldering iron. If anyone knows what needs replacing and can help, I will be obliged.
If anyone has a spare electronic switch circuit, that would be even better.

Many thanks.