Dear Beatriz and Rebeca,
the teams for languages other than English are created by the moderator of that language. This person chooses the subtitlers (also called subbers here) who will translate. The teams are formed long before a drama or film starts.
Some moderators look here at Discussions, and they may write to you.
But the safest way to go about it is to actively search for Portuguese moderators and send them a p.m. (personal message) asking if they can use you in any of their teams.
How to find the names of Portuguese moderators? That’s the easy part. You go on the main page of dramas and look at that loooong vertical picture with all info about the drama and the characters. If you scroll down, towards the end there is a table with all the names of language moderators.
If the page is done well, the name is also a link that you can click, and it will take you to the moderator’s profile page. Under her name and avatar picture you will see a little envelope. This is where you click to send a message.
If the name is not a link, just select it and copy it on the Clipboard. Then go to your profile page, look at the URL, and substitute your username with the moderator’s username.
Example: Suppose your username is eleonora and the moderator’s username is maria.
Your URL is like this: https://www.viki.com/users/eleonora
You make it like this: https://www.viki.com/users/maria
Be sure to include info about you, such as your knowledge and experience, how much free time you have and when, and whether you have Vikipass or not (it is important for new, on-air dramas, because they are most of the time behind Vikipass).
Of course you should write in Portuguese, so that she can also assess how well you write in your language. Be sure to spellcheck before hitting “Send”!
All the best