When you add a Safe Lives Assessment (SLA) to a case, it is automatically set to a due date of 56 days. The first time you add it to a case, you'll want to complete the SLA as quickly as possible, ideally on the same day. Once you have completed the SLA, ...
It's most likely that you haven't added the Closure Checklist to the case. Once this has been added and completed, an option will appear that will allow you to close the case.
This is probably because you haven't completed the new Assessment Checklist. Once this has been added and completed, the option to move the case to Ongoing Support will be added.