Redirection change HTTP with HTTPS

Hello,
I’m trying to create a hundred redirects from some old pages to retrieve their backlinks.

But every time I try to insert a link in “http” it is then changed to “https” and the original url is not redirected.

I’ll give you an example. I would like to redirect this url:

http://mydomain.com/index/offer/

here

https://www.mydomain.com

But when I put the first link inside your plugin and click on “add redirect” the first link is changed to:

https://mydomain.com/index/offer/

How can I solve?