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Having asked to give up Brazilian nationality is the one case the Constitution now addresses directly, and it addresses it in your favour.
Since the October 2023 amendment, a request of this kind is the only way a Brazilian by birth can lose their nationality at all — and the same amendment added a provision saying, in terms, that renouncing does not prevent the person from later reacquiring their original Brazilian nationality. So the door was deliberately left open behind you, and what is restored is the nationality you were born with rather than a naturalisation.
The application is reacquisition, made to the Ministry of Justice, with the documents its published schedule sets out. It is worth retrieving the declaration that recorded the loss, because its date and terms are what the application is built on.
One thing we would check before filing rather than after: whether reacquisition is still being made conditional on giving up your other nationality. The published guidance says it is, and allows a provisional grant with time to prove it — but that guidance predates the 2023 amendment, and sits awkwardly with the provision that expressly preserves your right to come back. How it is actually being applied is the question that decides whether this is straightforward for you.
Send us the date you renounced and details of the nationality you hold now, and we will establish which condition is currently being applied before you commit to anything.