If you want to edit your Post your options are to edit or add a Clip linked otherwise create a new Post!
From the Manage Posts view, select Change Clip from the actions:
Your list of Clips will be available & you can change which Clip is linked to your Post.
Of course you can always duplicate your Post & have a different Clip on each version if you are doing A/B testing of your CTA.
Go ahead, experiment!
Can't find your Post, read this article.