If I descended from a Jewish Woman, what would be the process of Teshuva?

I have been interested in “becoming” jewish for a long long time and, just now, I discovered that my great-great-grandmother lived in a 12-hour walk from the first jewish settlement in Paraiba-Brasil and, from her mother’s side, her surname was a Jewish one(Lopes).

I have to analyse the documents to see if this lineage is really jewish before I take any action(obviously), but, in the case it is, what would be my process of Teshuva?

Could I just enter in a Synagogue and start to pray? How could I find a group that would accept me? And for my religious duties: am I bound to keep Shabbat?

Thanks in advance for the answers!

Edit: this lineage is matrilineal, the mother from the mother from the mother etc