Hi Ziggy Zulueta,
Thanks for your patience and reply.
Please use Azure Portal, open your Azure Cosmos DB for MongoDB (vCore), go to Overview section as shown below and use option "Reset Password" to change password of your admin username:
As per the documentation here https://video2.skills-academy.com/en-us/azure/cosmos-db/mongodb/how-to-setup-rbac#limitations, a user's password can earlier only be set/reset by through the Azure CLI / Azure PowerShell which is now possible through Azure Portal too.
To update the user's password, send the new password in the password field.
In Powershell:
az cosmosdb mongodb user definition update --account-name <account-name> --resource-group <resource-group-name> --body {"Id":"test.myName","UserName":"myName","Password":"pass","DatabaseName":"test","CustomData":"Some_Random_Info","Mechanisms":"SCRAM-SHA-256","Roles":[{"Role":"My_Read_Only_Role101","Db":"test"}]}
Please try and let us know if you could make it or face any issue.
Awaiting you reply so that we can assist further.
Thanks