dónde podría cambiar el display del reloj .
Where could I change the clock display?
Ask Garmin at https://support.garmin.com. Possibly it is because a swollen battery pressing against the display, and replacing the battery would fix it. Search YouTube or Google for the term "battery exchange" and the watch model name - on some models it is possible doing it yourself, on others soldering is required, which may not be easy for someone without experience.
There are some older threads related to the "white spot" issue. For example - White spot on Garmin Forerunner 245
Depending on the warranty status of your watch, there's a chance that Garmin offer to replace it or offer a discount on a refurbished watch.
As trux suggested, best to contact Garmin Product Support directly for assistance, if repairing it yourself is out of your wheelhouse.