In order to enable release synchronization you need to find the integration settings in StoriesOnBoard:

Then on the integration settings tab, scroll down to the Card synchronization part and make sure, that the Release synchronization checkbox is checked (if it isn't, check it and click Save):

On the Jira side, you need to find the "Features" tab and enable Releases & versioning:

In case that is the first time you are enabling this setting, you need to go back to StoriesOnBoard and validate the configuration, the click Save.