Upload the new translated strings

In Portuguese, the string is correct I just don’t want to overwrite it when I upload the new translated strings done in Brazilian Portuguese.

I want to upload from Brazilian Portuguese the strings that are not yet translated in Portuguese, I don’t want to do it manually each time

You can download the file in XLIFF and translate it locally

Once the translation is finished, you can just upload the translated file back to the project in “Translations tab” with “Upload translations” button
upload

If some translations are already added in Crowdin project, they will be saved after the upload of the translations. The string will just have 2 or more suggestions

Once you add the translation in XLIFF file, change the target state from “needs-translation” to “translated”

So translated string should have:
<target state="translated">YOUR TRANSLATION</target>