Reckon, as before, you'll have to give further consideration to (5,5)
I believe the answer is:
think again
'reckon as before you'll have to' is the definition.
I know nothing about this answer so I can't judge whether this works.
'further consideration to' is the wordplay.
I cannot quite see how this works, but
'further' could be 'again' (I've seen this before) and 'again' is found in the answer.
'consideration' could be 'think' (think is a kind of consideration) and 'think' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'give' acts as a link.
Can you help me to learn more?
(Other definitions for think again that I've seen before include "Reconsider" , "have another brood?" .)