Need help installing this plugin

Hello,

I’m not a web developer or coder or any sort of computer scientist. I was hired by someone to help develop their wordpress site more. Since the latest wordpress update, apparently this has broken some of the plugins on the site and the issue is a “swipebox” that turns the whole screen black when I try to click on anything. I saw that this plugin can be used to temporarily fix the broken plugins so I can log in an disable them.

I have no idea how to install and use this plug in though. It says to upload it to wp-content/plugins/ but how do I access that if I can’t even log in to my site (because the whole screen turns black). I saw somethings mentioned of using cPanel or myPHPadmin, but I have no idea how to use these software or how to even install them either. My client is an older person and doesn’t know much about technology (much less than myself), so doesn’t know any of the server information anyways.

My client is really upset with me and thinks I broke the website. Does anyone have any ideas how I can fix these broken plugins and get into my site?

The page I need help with: [log in to see the link]