You can access the general settings in two ways on the web app. The first one is when you are in the library, go to the top left of your screen and click on the setting icon.
Are you already in a Sendsteps and do want to change your settings? Click on the setting icon in the left corner next to your Sendsteps name.
PowerPoint Add-in
In the PowerPoint Add-in there is a menu with the setting button. Click on this button to go to the general settings when you are using the add-in.