how can I unlink a domain user from an azure subscription and link it to a new user with a new directory

@Jorge Arquillo ,

Usually users who are able to perform activities with an Azure Subscription, are ideally added to the Access Control(IAM) section under the Azure Subscription blade. Hence you can go to the IAM section and then remove the user from the "Role Assignment".

For the next step, you would have to transfer the subscription to the next tenant. Transferring the subscription would allow you to add the users belonging to that new Tenant or directory under that new tenant.
You can refer to the following article for more reference: https://video2.skills-academy.com/en-us/azure/active-directory/fundamentals/active-directory-how-subscriptions-associated-directory

Hope this helps. Please do mark this response as answer in case this response helps in answering your query. If not do let me know if there are any more queries around this, so that we can help you further.

Hello soumi-MSFT,

I have created a new tenant and I have transferred the domain subscription but I am still entering with the same user. I have not seen the option to unlink the user and be able to enter with another user.

I want to log in with a user that I created again at outook.com. It's possible ?

Thank you very much and greetings