Not sure if this will help find him if this was his Regiment/Battalion?
"66TH FOOT REGIMENT (2nd Battalion)
This battalion of the 66th Foot Regiment arrived in St. Helena from England between April 20th and
May 13th 1816,
in the transports David, Martha, Retriever, Amity, Abona, Queen, Regulus"...
From...A St. Helena Whos Who - Forgotten Bookshttps://www.forgottenbooks.com
Annie