Bubble lets you revert changes to your application in case something went wrong. For instance, if you deleted a page and want to get it back, or realized that a change you pushed alienated your users, etc.
You can revert your app based on your plan. Some plans offer more history than others, but the mechanism is the same for all users.
As explained above, your application has two versions. The development version is the one you work on, while the live version is read-only and the one your users interact with in production. You restore your application in development mode, and if you need to deploy an older version of your application to production, you then deploy (push) to live (see above for more details).
The panel that lets you revert to an older version is the same as the one that lets you deploy your development version to live.
The lower part of that popup shows the previous deployment, with the description you've entered then, and the previous reverts, if any. To revert you development version, enter the time (in your time zone) you want to revert your development version, and press 'Revert to this time'. It is important to note that deploying and reverting app version does not affect the actual database (the things your users have created). However, it will copy (or revert) the data types, as they are part of the application.
Each entry is the previous deployment table lets you copy the time to the input for convenience. Clicking on the button will populate the input with that time, and you'll just need to click on 'Revert to this time' to revert your app.
You can revert a restore that went wrong by reverting your app slightly before the wrong restore happened.