My friend water damaged his samsung galaxy watch active 2. The symptoms - not working power button (was working erratically before stopped working altogether). Before sending it he shot a couple photos showing a weird green blob [1] on the flex cable connecting power button to board which promptly broke off [2] taking trace with it. Also corrosion was visible on solder joint of the flex cable.
Then I got the watch in my hands. It disassembles easily with no glue and somewhat specific Y00 screwdriver. Sadly I didn't take photos of the disassembly but there are many nice guides with photos on the internet.
First i tried to bridge the broken trace with a jumper [3]. This didn't restore functionality of the button, since the pad was corroded. The flex cable could be lifted from the corroded pad - it was not soldered.
The cable was desoldered and the pad exposed [4]. With some careful scraping copper surface was revealed and the pad was tinned [5]. While the cable was desoldered I decided to take a picture of its bottom [6] showing the corrosion.
After the pad was tinned I ran a similar jumper, but this time reaching the pad [7]. After reassembly the button worked.
It would be interesting to hear what you think that green blob was and overall feedback is appreciated.