No, you can't transfer reservations between partners or providers. You would have to refund the reservation and then re-purchase it for the new partner if it is still required.
https://learn.microsoft.com/en-us/partner-center/transfer-azure-subscriptions-under-azure-plan
Right now, there is no penalty fee for this but in future refunding may incur a 12% penalty fee.
https://learn.microsoft.com/en-us/azure/cost-management-billing/reservations/exchange-and-refund-azure-reservations#cancel-exchange-and-refund-policies
****UPDATE:** Transfer of reservations is now possible.** This has very recently been announced. Please see below link for info:
https://learn.microsoft.com/en-us/partner-center/announcements/2022-february#21