You can block yourself by following these steps:
1) Within Synergetic, click Students
2) Click Parent Teacher Interview Maintenance
3) Type the current year (eg 2020) in the PTI Cycle Code field and click OK.
4) Click the Sessions tab, and select the session you're wanting to block out (e.g. Junior School Session 1)
5) Click the Staff button over on the right, then click Availability
From there you can block yourself out by unticking the tick boxes next to that time