Creating a new part from a mold?

Hello there, I've been using the student edition for about a month and I am pretty new to the software.

I found out how to make a "mold" in assembly mode if you already have the part (Model > Component > Component Operations > Cut Out)

But what if I need to go through the opposite process? I have the mold and I need to create a new part out of it.

Any help? Thank you.