In Kashmir, the UN itself demanded such a vote but India after 72 years has always refused to allow the UN to mediate on this matter. This has led to endless conflict including two Indo-Pakistani wars, hundreds of thousands of deaths, abuses and incarcerations.
You may be interested in these active petitions
A UN supervised plebiscite is their right!
Many indigenous minorities within India have been denied their right to self-determination but are attempting to initiate plebiscites e.g. the Sikh Referendum 2020.
India has now escalated the conflict by withdrawing Kashmir's special constitutional status (Article 370) and attempting to absorb the region as a 'Union' territory.
Article below is a statement of Kashmir's Self Determination Struggle:-
https://www.dawn.com/news/1513347