Manipulate boards to gain the ascendancy (4,3,6)
I believe the answer is:
turn the tables
'manipulate boards' is the definition.
I can't tell whether this defines the answer.
'the ascendancy' is the wordplay.
I cannot quite see how this works, but
an anagram of 'the' is 'het' which is located in the answer.
The remaining letters 'turntables' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'to gain' acts as a link.
Can you help me to learn more?
(Other definitions for turn the tables that I've seen before include "Make a complete reversal" , "effect complete reversal" , "Reverse the positions" , "Reverse fortune" , "Achieve complete reversal" .)