The mixed Content issue is causing problems in admin side.

I just activate SSL on my site. However, the admin-ajax is still served over HTTP and there is some mixed Content issue in admin side causing problems like cannot add, delete plugins, edit posts/pages with visual composer and so on. Please help.

https://static.livechatinc.com/8801096/P9RX5TVSFR/614dd84c1274a021fd801c6b502cb8bc/Screen%20Shot%202018-06-07%20at%2012.27.50.png