How soldiers may move part of foot (6)
I believe the answer is:
instep
'foot' is the definition.
(thesaurus)
'how soldiers may move part' is the wordplay.
I cannot quite understand how this works, but
'move' could be 'step' (stepping is a kind of moving) and 'step' is found within the answer.
'part' could be 'in' (synonyms) and 'in' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
(Other definitions for instep that I've seen before include "One part of Oxford" , "Part of foot (how to march!)" , "Foot arch - conforming" , "Arched part of foot" , "Upper surface of the foot" .)