If you don't see option to create a new Data model or update an existing one, there's a chance that your user account is missing the required roles.
Let's see what roles are required to create Data model in Oracle Fusion BI Environment.
To get Data model access, create a new custom role and map the below roles to the custom role.
=> BI Consumer Role
=> BI Publisher Data Model Developer
Assign this custom role to your user and you should get the access to create a new Data model or edit an existing one.