I found this instruction how to take apart the Forerunner 735XT very helpful:
https://de.ifixit.com/Teardown/Garmin+Forerunner+735XT+Teardown/117852
I have several Forerunner 735XT whatches which do not work, which I bought on ebay as replacement watches. I asked myself, how to repair them. I found also this video very helpful, how to repair water damaged Vivoactive HR:
https://www.youtube.com/watch?v=rAKbZ_Txm1E
Is not the major cause that a Garmin whatch stops working a water damage? Try to repair it by opening the watch, an blow the water out with a air pressure spray.
Is Garmins marketing about water resistance of their watches misleading? I read about frustrated users in the forum disappointed that their watches stopped working after use in water.
Should not Garmin be more clear about water resistance? Should Garmin not change their marketing by stating "Garmin garanties water resistance during waranty time", and not more, and not less?