While configuring your workflows, meetings workflows, reports, and approvals, you see the button "Send Sample Message".

The "Send Sample Message" button helps you review what the Slack alert will look like when it is actually triggered.
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However, you will not be able to push any changes in Salesforce with the alert that is triggered as a sample message.

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So, you can click the button as many times as you want without worrying about editing your Salesforce data 😀