Thanks for reaching out to us. This is a great question.
I suspect what happened is that you have opened the strategy directly from the list of rules (Revision Management) instead of opening it from a change request. If you watch the solution video at: 01:37 you will see that the strategy is opened from the change request. In that case, Save button should be available to you.
As you advance in the course you will understand the difference, but for now, it is more than sufficient if you just focus on the strategy change.