Alert rules are an essential part of Missions and Mission templates.
Add Alert rules to a Mission template
When you create a new Mission template, you can set Alert parameters for it under Alert rules. All Missions created using this template will inherit these Alert rules.
Add Alert rules to an existing Mission
If you want to add new Alerts to an existing Mission, you can do so by clicking Edit mission on that mission's page. Check how to edit existing Missions for more details.
Under Alert rules, click Add new alert rule. Note that you can't edit existing Alert rules but you can add new ones.