First let's see the qualifying percentile for Scheduled Tribe for the previous years. The stats for the ST quota for JEE Main in previous years are:

2021: 34.6728999
2020: 39.0696101
2019: 44.3345172

So, according to the stats, you'll be qualifying the JEE Main easily. Now, the best colleges that you may get are:

NIT Silchar
NIT Mizoram
NIT Nagaland
NIT Arunachal Pradesh

You can also use our college predictor to see your chances in all the colleges:
https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

Hope I have answered your question. All the best!