In order to set up integration of Chat for Jira Service Management with Slack, first you have to create an app in your Slack workspace. Follow these steps to set it up:
Subsequent pages describe required setup for the above.
In addition to the above settings, you may wanty to set up an icon for your app. This icon will be displayed whenever the app posts any message to Slack.
This is done at the Basic Information subpage of your app:
You can use this icon for this purpose: