Fix SSL problems in Wordpress
Fix mixed content error in Wordpress in ALL pages of the website.
Yes, it will surely affect your rankings. That is because Google treats Http and Https version of the page as different pages, so if you don't set up the SEO correctly, you will risk losing all your hard-earned rankings. You can choose the option Seo Migrate if you want me to take care of this!
Technically is true: I will install a plugin. But this plugin won't make magic things if you don't set up the correct URLs in Wordpress and in its Database. I urge you to try it out yourself: install the plugin and check if it fixes the issues. If not, I will help you :)