Azure AD B2c - Custom Policy claims

I've been trying to configure my Azure AD B2C to use custom policies.

I managed to make it work by following this link:

https://docs.microsoft.com/en-us/azure/active-directory-b2c/active-directory-b2c-setup-commonaad-custom

The problem I have is:

The "oid" claim returned when i authenticate with a Microsoft Account is the Object Id created to the user in my B2C directory. I need to add the claim of the object ID from the original tenant. Any help on how I could do that?