Dealt with the forms when one acted as locum (6,2)
I believe the answer is:
filled in
'dealt with' is the definition.
The answer and definition can be both to do with communicating as well as being past participle verbs.
Maybe you can see a link between them that I can't see?
'forms when one acted as locum' is the wordplay.
I cannot really see how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'as' could be 'in' (I've seen this in other clues) and 'in' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'the' is the link.
Can you help me to learn more?
(Other definitions for filled in that I've seen before include "informed?" , "Acted as substitute" , "well-informed" .)