Here is the fragment again:
The man whom Brenda refuses to marry even if someone paid her a million
dollars.
You correctly identified the fragment as an appositive. The man whom ... is a noun phrase beginning with man, a noun.
To fix this fragment, you could add a subject and verb, like this:
Jeremy was the man whom
Brenda refuses to marry even if someone paid her a million dollars.
Or you could use Punctuation Rule 9 to fix the problem. Punctuation Rule 9 requires that you separate the appositive from the main clause with comma(s), like this:
Jeremy,
the man whom Brenda refuses to marry even if someone
paid her a million dollars,
never wears socks that match.
Or like this:
Over in the corner sat Jeremy,
the man whom Brenda refuses to marry even if someone
paid her a million dollars.
Enjoy your your visit to the Queen's garden!