The most common and most likely answer to this crossword clue is the 5 plus 2 letter word BRUSH UP
I've seen this crossword clue in The Guardian
B
R
U
S
H
U
P
More clues leading to the result BRUSH UP
Buddy explains!

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 BRUSH UP mean?
BRUSH UP noun- A slight correction or modification.
- A review of a topic to be learned.