Please clarify your question. You cannot edit a PPT slide imported in Captivate, the whole slide will be a movie slide replicating eventual animations set up in PPT. You don't have access to individual objects.
When I try and edit a PowerPoint slide imported in Cpativate, I get a gray screen; so instead of showing me the slide in PPT si i can make changes, I get a gray screen. It appears as if Cpativate and PPT have stopped commincating. I've attached a screen shot. I'm using Win 10 and the lastest versions of PPT and Captivate 2019.
When I see tutorial video on using this feature, the author clicks Edit > Edit with Microsoft PowerPoint > Edit Presentation. Then, the slide opens in "PowerPoint" (but within Captivate) and edits can be made to text.