Firstly check that the watch is charging when you have it plugged in. Press the SOS button once to light up the screen and you should see the battery charging symbol. This is to ensure there is no problem with the charging cable or the socket you have it plugged into.
Next hold the SOS button for about 10 seconds to see if the watch will power on.
To rule out damage to the charging cable, if you have a Samsung phone, you could use the Samsung charging cable to try to charge the watch to see if that cable charges the watch.
Try charging the watch using a different socket or test the socket you are using with another appliance to confirm the socket is working correctly
Check if there any sign of damage to the watch or could water have gotten into the watch.
Do a visual check of the charging port to see if there is any sign of damage to the inside of the port. The cable may not insert into the charging port or be loose when inserted into the charging port. There may be signs of damage on the end of the charging cable.
Please contact firstname.lastname@example.org with the results of the above checks so we may assist you promptly. Where you think there may be damage to the charging port, please provide a clear, close up photograph of the inside of the charging port.