It’s actually quite easy, you just need to go to this page, then include these information:
• Are you an admin of the parent Company Page?
• Are you an admin of the Showcase Page that you’d like to deactivate?
• Showcase Page URL
• Reason for request
Note that admin approval is needed to deactivate a Showcase Page.
Within 2 hours, I got a reply from LinkedIn staff:
I’ve gone ahead and removed the Showcase Page. Please know that the name will not be available for future use. If you or your organization would like to reestablish this page later, please contact us for reactivation.
If there is anything else I can help you with, reply back to this message and I’ll gladly follow up with you.
Have a great day!
LinkedIn Customer Advocate
So actually you can’t delete a Showcase Page instead deactivate it with the help of LinkedIn staff. The thing is, their support is quick and pleasant and I’m thankful for that. But why can’t users deactivate it by themselves?