Hello, thank you for reaching out to Microsoft Q&A.
You cannot transfer an Office 365 Subscription from one account to another.
So, sign in with your @gmail.com account on the Services & Subscriptions page here to cancel your Office 365 Subscription.
https://account.microsoft.com/services
(select Manage Subscription > Then Cancel Subscription)
Once the cancellation is complete, you will receive a confirmation email about the refund, and the amount will be credited to your original payment method within 3–5 business days.
You can then purchase a new subscription using your @outlook.com account.