Foolishly, I err -- second needed to think again (10)
I believe the answer is:
reconsider
'to think again' is the definition.
('consider' is an answer for 'to think' so perhaps 'reconsider' is OK for 'to think again')
'foolishly i err second' is the wordplay.
'foolishly' is an anagram indicator.
'i'+'err'+'second'='ierrsecond'
'ierrsecond' with letters rearranged gives 'RECONSIDER'.
'needed' is the link.
(Other definitions for reconsider that I've seen before include "Nice orders ( anag.)" , "Ponder further" , "Have second thoughts" , "Think again" .)