Submission issuer occasionally supports to soften things up (9)
I believe the answer is:
tenderise
'soften things up' is the definition.
(to tenderise is to soften)
'submission issuer occasionally supports' is the wordplay.
'submission' becomes 'tender' (tender can mean a submission or bid).
'occasionally' indicates alternate letters.
'supports' is a charade indicator (letters next to each other) (bottom letters provide a support for the top ones).
The alternating letters of 'issuer' are 'ise'.
'tender'+'ise'='TENDERISE'
'to' acts as a link.
(Other definitions for tenderise that I've seen before include "pound" , "soften flesh" .)