How to Combine two OTM/GTM users into one Cloud SSO user

It is often that certain OTM/GTM user needs to be both DBA.ADMIN and an ADMIN user in his/her company's specific domain. The quickest way is to set up two OTM/GTM users with two separate emails to login. But there are cases where the Federated SSO only allows one user per person. In general we can use Grant but getting a user/role to grant access to another user/role is another domain can be tricky.

Hence the question: How to Combine two OTM/GTM users into one Cloud SSO user