If you've opened your Powtoon in the Studio and do not see the tabs (on the right side of the screen) or the timeline, your Powtoon has been opened in Edit mode, as in the screenshot below.
When you are working on a Powtoon based on a template, this is the mode in which the Studio opens (by default).
If you'd like to add the tabs and timeline back to the Studio, open the Studio modes drop-down list and select Create Mode.
If you'd like to add the tabs and timeline back to the Studio, open the Studio modes drop-down list and select Create Mode.
The Studio mode will change to Create Mode, and the tabs (Scenes, Background, Text, etc.) and timeline will be displayed on the screen.