If you're using Fusion for education, this feature will work differently for you. Scroll down to Work with milestones and versions in History (Fusion for education) to find out how.
Fusion tracks iterations as versions and changes. Use the History dialog to access them.
(Optional) In the History dialog, select which types of changes you want to see.

Place the pointer over the timestamp that corresponds to the change or version you want to open.

Click the timestamp to open that version or change.
Fusion for education tracks iterations as milestones and versions. Use the history dialog to access versions and create and manage milestones.
The component History dialog displays.
In the Fusion web client, navigate to the Overview tab on the design details page.
Click the version control drop-down.

The History dialog contains a list of versions and milestones of a component.
Select a version you want to work with.
In the upper right corner of the dialog, click More
.
Select an option to create, edit, or navigate to a milestone.
Fusion options include:
options include: