Yoast SEO disappeared and cannot be reinstalled

My Yoast SEO plugin disappeared from the plugins and cannot be reinstalled. When I try to install it it says, the installation folder has been found and that’s why the installation could be finished. How can I solve this? Where is this folder and how can I remove it to install the plugin again without losing all my SEO titles etc.? And why in the world did the plugin disappear in the first place?
Thanks for your help!