After creating your operation groups you can start setting up the maintenance plan for a specific group of assets.
First go to the admin home page and head over to the “Maintenance” section. Click on “Maintenance plans” and, on the next page, click on the green “add maintenance plan” button to create a new maintenance plan.
In the form that appears next you can
give your new maintenance plan a name and
select the counter types that should be activated for the assets.
Next, choose the operation groups that should be part of the maintenance plan and save your new maintenance plan by clicking on the blue "Save" button at the top of the page.
For the maintenance plan to be applied to your assets you'll need to assign it to the relevant rolling stock in your fleet. This article explains how you can do so: Assign a maintenance plan to your assets