Since order messed up, have another think (10)
I believe the answer is:
reconsider
'think' is the definition.
(I know that reconsider is a more specific form of the action consider)
'since order messed up' is the wordplay.
'messed up' is an anagram indicator.
'since'+'order'='sinceorder'
'sinceorder' with letters rearranged gives 'RECONSIDER'.
'have another' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for reconsider that I've seen before include "Think again" , "Ponder further" , "Nice orders ( anag.)" , "Have second thoughts" .)