Decide to check what's suitable (3,3)
I believe the answer is:
see fit
'decide' is the definition.
(thesaurus)
'check what's suitable' is the wordplay.
'check' becomes 'see' (synonyms).
'what's suitable' becomes 'fit' (similar in meaning).
'see'+'fit'='SEE FIT'
'to' is the link.
(Other definitions for see fit that I've seen before include "Perceive in good shape, so choose to do?" , "Consider appropriate or choose to do" , "Want" , "Consider to be proper or desirable" , "Think suitable" .)