You can revert any change you want by clicking revert on the left side of every change. To save your changes just click Save button. You will see that Status of every issue changed to Success and Changelog was cleared. If one of the changes can't be saved its Status will change to Error and error message will be shown.
You can also revert all made changes if you don't want to save them. Just click Revert button.
You can edit date and time in Changelog. Just click the pencil icon and the pop-up calendar will appear.