If you wish to disable Slack notifications, simply navigate to the Slack page in Myndbend Process Manager admin app, and click on Configure button in the top right corner of the page:
On the configuration page, disable the "Enable Slack Approvals" setting, and save the settings.
Notifications will no longer be sent.
Note: This does not revoke the connection between your Slack and your Myndbend account. If you wish to fully revoke the access, you will need to revoke the access in Slack app directory.