Does the pod need to be off center like you have it or should it be centered?
Maybe something like this?
I created a “cutter” shaped like the pod but I extended the top a bit and added a “drill” for the bottom hole. This is a simplified version of the pod because a lot of the detail around the top isn’t needed. The additional height on top and bottom isn’t critical but making it extend well beyond the other part makes cleanup easier.
Than, as Steve wrote, using Intersect Faces and erasing the unwanted bits will leave you with the adapter. I copied the cutter into the K-cup component and exploded it. Then I made a copy of that component and used the Dave Method before the Intersect operation to ensure that the result is a solid.
The K-cup component is nested in an unnecessary wrapper so explode the outer one.
FWIW, assuming the pod is exactly the right size, it wouldn’t fit in the adapter if you make the opening the same size. I enlarged the cutter a little to make some clearance.