Convert existing commercial M365 subscriptions to nonprofit discounted subscriptions

Question

I have several Microsoft subscriptions on an existing Microsoft domain mycompany.com, but recently signed up to be approved as a registered non profit to receive access to the discounted subscription offers and during that process, Microsoft had me create a second domain e.g. mycompany2.onmicrosoft.com. How do I merge these two domains into one so I don't have to deal with two logins and how can I transfer my existing commercial subscriptions to the nonprofit skus available?