Upvote:1
There's no specific guidance on this that I'm aware of.
In the past, I've addressed the letter to the appropriate High Commission, the salutation being "Dear Entry Clearance Officer". As Moo has suggested in the comments, "To whom it may concern" is also an option.
Whichever form of address you choose, it's quite unlikely to materially affect your application; it's the content of the letter that really matters.