If you were born before 1 January 1983
You became a British overseas territories citizen on 1 January 1983 if both of these applied:
you were a citizen of the United Kingdom and Colonies (CUKC) on 31 December 1982
you had connections with a British overseas territory because you, your parents or your grandparents were born, registered or naturalised in that British overseas territory
You also became a British overseas territories citizen if you were a woman married to a man who became a British overseas territories citizen on 1 January 1983.
https://www.gov.uk/types-of-british-nationality/british-overseas-territories-citizen
Hong Kong
If you were a British overseas territories citizen only because of your connection with Hong Kong you lost that citizenship on 30 June 1997 when sovereignty returned to China.
However, you became a British overseas citizen if either:
you had no other nationality and would have become stateless
you were born on or after 1 July 1997 and would have been born stateless if one of your parents was a British national (overseas) or British overseas citizen when you were born
https://www.gov.uk/types-of-british-nationality/british-overseas-citizen