The most common and most likely answer to this crossword clue is the 7 letter word REMOUNT
R
E
M
O
U
N
T
Buddy explains!

The straight part
We know that "get back on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case get back on = remount.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 REMOUNT mean?
REMOUNT noun- The opportunity of, or things necessary for, remounting; specifically, a fresh horse, with its equipment.
- The process of mounting a drive or volume again.
- The restaging of a play or film.
- To go up again; to rise another time.
- To help (someone) back on a horse.
- To get back on a horse, bicycle etc.
- To get back on (an animal, vehicle) again.
- To ascend (something) again.
- To fix (something) back into position.
- To mount (a drive or volume) again.