When you install BubbleIQ, it automatically allows you to edit standard ticket fields. BubbleIQ also supports the ability to edit custom Zendesk fields from Slack.
To enable it, have the BubbleIQ admin message the bot "admin", and click "Select and Add Custom Fields". Then select "Enable Custom Fields" as true, and pick the fields you'd like to enable.
You'll now see a custom fields button on all tickets in Slack. Click it to edit those custom fields for that ticket.
That's it! You can also specify if admin users or all users can edit custom fields.