To delete/revoke Slack Authentication to re-authenticate in Salesforce, check the following steps:

1. Go to Settings.

2. Select Slack User Mappings.

3. Use Delete Action to Slack Authentication to re-authenticate in Salesforce.

To re-authenticate, please check the following:

https://www.infallibletechie.com/2022/10/how-to-authenticate-service-cloud-for-slack-salesforce-app.html