For Slack integration navigate to Settings >> Integrations tab.

Connecting Slack & UpRaise

Click on Add to Slack & you will be navigated to authorize UpRaise access to your Slack details. The scope of this access will be visible on the authorize page. This is how the page will look like.

Once authorized you will be navigated back to the UpRaise settings page. On integration page, you should now see Slack integration in connected state which is why you find an option Disconnect Slack on this page.

Disconnecting Slack & UpRaise

When in connected state, Disconnect action against Slack integration is displayed (above image). Click on that button & connectivity between UpRaise and Slack will no longer exist.