Once more become involved with new ‘green’ era (2-6)
I believe the answer is:
re-engage
'once more become involved with new' is the definition.
I can't tell whether this defines the answer.
'green era' is the wordplay.
I cannot really see how this works, but
an anagram of 'green' is 'reeng' which is located in the answer.
'era' could be 'age' (I've seen this before) and 'age' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for re-engage that I've seen before include "Get back on job" , "Employ or hire again" .)