You can perform the downgrade using the script editor in SANtricity Storage Manager or the SMcli. You will specifically need to use the Downgrade option. See this guide.
I also want to point out the warning from that page:
Attention:Possible damage to the storage array configuration – Downloading a previous version of the controller firmware or NVSRAM incorrectly can result in damage to the controllers or a loss of data access. Contact technical support before using this parameter.