Hi @Khrystyna
The trigger part is easy, you can use any of the Slack Triggers available (I won't be a button but it would be like a certain message, maybe to a private channel?)
The Salesforce part on the other hand is tricky. There isn't an integration to create cases, so you will probably have to build your own private integration using Zapier Developer Platform https://developer.zapier.com and Salesforce API documentation.
Hi there @Khrystyna -coming in to see how you’re coming along with Moh’s advice above. Let us know if there is any more detail we can send your way, or vice versa.