Mirador de Abrante above Agulo in La Gomera's north (Archive)
Sadly new 'health control' regulations apply when going to Spain and that includes La Gomera. All travellers now must complete a form and then a unique personal QR code is generated which can be used in printed form or downloaded with an app. The registration form should be downloaded, completed and returned BEFORE you travel to avoid delays at airports. The generated individual code must then be used wherever you go in Spain.
Here's the link to the official Spanish health ministry's website (in English) with all the relevant information and from where you can proceed: https://spth.gob.es
Note: All La Gomera Ferry services still run a reduced schedule which changes frequently, and health-bureaucracy is strictly enforced on arrival and departure in all Canary Islands ports, so allow a bit of extra time if planning a trip.
Also the Canarian government does still plan to go ahead with mandatory testing of incoming tourists at airports despite the Spanish government ruling this out, so it remains unclear what happens on arrival in the Canaries. Not very inviting, really, on top of all the rest of the hassle.
...and by the way La Gomera has NOT had any Covid cases for ages.