You can refer to the following steps:
- Create a new command channel in SCOM
- Attach a script that will process the alert output (logic that transforms the data and sends it to Slack)
- Create subscriptions for monitors and rules to be delivered to deliver the command channel to the subscription
If you have Orchestrator in your System Center infrastructure, you can trigger runbooks by SCOM alerts. It's a great way to make the process more manageable. You can invoke the script in the runbook.