To temporarily disable Slidewise in PowerPoint do the following:
- Click the Insert tab, and then click the down chevron next to My Add-ins.
- In the View and manage Microsoft Add-ins dialog check that COM Add-ins is selected in the dropdown and click Go...
- Uncheck the box alongside Slidewise, click OK.
If you need to fully remove Slidewise for good then you need to read how to uninstall Slidewise.