Your gas strut has lost its pressure.
I have two replacement struts in inventory (not going to re-order any more since my store is closing). $ 65 each + $ 10 shipping. That will restore the function. Go to this page to order if you like, you will see it on the bottom of the page. https://keepingroom.com/leather-care Fill out the request and I will email you an invoice. You can do this yourself in 15 minutes. See the photos below. I use a plastic automotive trim removal tool to not mar the leather when popping the panel off the tacks, you *can* use a screwdriver, but you will mark the leather. Trim tools are $ 5 at Amazon
https://www.amazon.com/KINGLAKE-Pane.../dp/B00HNMLQAG
Duane Collie
Straight answers from thirty-six years in the business.
My Private Messages are Disabled - Please ask questions here in the forum.