The most common and most likely answer to this crossword clue is the 10 letter word MANIPULATE
I've seen this crossword clue in The Guardian
M
A
N
I
P
U
L
A
T
E
More clues leading to the result MANIPULATE
- Exploit chap I turned out of bed past time
- Engineer chappie on island turned up dead
- Work with football team keeping one quiet long into the night?
- Crikey—I turned up late for work
- Met Al up in Ambleside about upcoming work
- Redesign planetarium without right engineer
- Couple carry a flower over to doctor
- Fix for rival to lose head, having drunk a little whisky?
- Handel in conversation with doctor
- Doctor seeing bloke out of bed, one heaven-bound, dead
Buddy explains!

The straight part
We know that "Fix" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fix = manipulate.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 MANIPULATE mean?
MANIPULATE verb- To move, arrange or operate something using the hands
- To influence, manage, direct, control or tamper with something
- To handle and move a body part, either as an examination or for a therapeutic purpose
- To influence or control someone in order to achieve a specific purpose, especially one that is unknown to the one being manipulated and beneficial to the manipulator; to use
- To use the hands, especially in scientific experiments.