Yes, it is possible to allow external, not licensed users to fill in their part of the workflow using the Field Service app in Odoo. Here are the general steps you can follow to set this up:

1. Go to the Field Service app and click on "Configuration" and then "Teams"

2. Create a new team and assign the subcontractors to this team

3. Go to "Work Orders" and create a new work order and assign it to the team created in step 2

4. In the work order, you can add the input fields that the subcontractor should fill in.

5. You can also set permissions for the subcontractors, so they can only access the work orders that are assigned to them.

6. Once the subcontractor fills in the input fields, you can review and approve the work order.

Please note that the above steps are general, and the process may vary depending on the version of Odoo you are using and your specific setup. You may need to consult the documentation for further information on how to set up the Field Service app in Odoo.

Alternatively, you can consider using the "Project" app in Odoo, which allows you to create a project and assign tasks to external users. You can also set permissions for the external users, so they can only access the tasks that are assigned to them.