For your Magento Commerce Cloud project, you may change the New Relic account owner on the New Relic UI page. For detailed steps, see Change the account Owner (New Relic documentation).
If the user (that you want to assign the owner role to) is not listed on your account yet, you will need to add the user to the account. See Add and update users article, in particular the Add a new user section (New Relic documentation).
If someone needs to be added as a user but no existing Owner or Admin on the account can help them, any Magento user who has access to the New Relic's Magento Partnership Owner Account is able to view all Customer accounts and add users on the Customer's behalf.