Tidy mess made by Englishman in Australia, as it were (3,2)
I believe the answer is:
mop up
'tidy' is the definition.
The answer and definition can be both related to change as well as being verbs in their base form.
Maybe there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for mop up that I've seen before include "Finish a task, clear away remnants" , "Kill (enemy stragglers)" , "polish off" , "take care of" , "Clear away, dispose of" .)