Factory pattern where concrete classes are on separate DLLs

I wrote a dlls that connect to some 3rd party API, each DLL has the methods: SignIn,Upload,Download,SignOut.

My manager asked me to implement a factory pattern because in future I will write more dlls to other APIs that has the same methods signuture.

I have never used this pattern so I have some questions and need some guidnes.

For now I have:

DLL 1: OneDrive

It has a class with methods: SignIn,Upload,Download,SignOut.

So if I want to use it I'm adding reference to this DLL and then any app can use this DLL.

DLL 2: DropBox

It has also class with methods: SignIn,Upload,Download,SignOut.

My question: How do I implement the factory method design pattern in this secnario?

What I did: I created another DLL("The new DLL") this DLL would contain the "FactoryClass", the problem is that the creator in this dll should return a type of "OneDrive" or "DropBox" that means I should add refernce to the first two dlls ("OneDrive" and "DropBox").

But, The classes "OneDrive" and "DropBox" should implement some abstrct class whithin the new dll that means I should add refernce to the new dll.

but it's not possible because it's circular dependency (Visual studio error)