The most common and most likely answer to this crossword clue is the 8 letter word REFINISH
I've seen this crossword clue in The Guardian
R
E
F
I
N
I
S
H
Buddy explains!

The straight part
We know that "cover again" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cover again = refinish.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does REFINISH mean?
REFINISH verb- To finish again; especially, to apply a fresh finish, as a new coat of varnish or paint.