We're using a custom Slack app, the People Connect Bot to setup the connection between Slack and GitLab Service Desk for the People Experience team.
The bot is setup to only look into one channel (the "People Connect" channel). Every time someone adds a new message to this channel, the bot will pick this up and create a new issue on the private GitLab People Connect project. This project is also set up to use Service Desk with a specific email.
When a PEA adds a note to an issue started by a Slack comment, a GitLab webhook will be triggered to the People Connect bot and this will add the note as a comment on the Slack thread. When the team member replies, this will trigger a note on the ongoing issue and so on.
In case the PEA closes the issue and the team member replies to the thread, the issue will be reopened. This way no issue gets lost.
Issues with the bot and/or feedback about the process can be created here