https link for http website

Dear all,

My curiosity has brought me an issue with my website. I haven’t used my website for a while and was updating it lately. My website is a http website, and I am planning to move it to https (although I’m yet not sure how to tackle that).

In my curiosity, I wanted to see what would happen if I would change the link in the settings from ‘http://sannesteen.nl’ to ‘https://sannesteen.nl’. I know what happens now: the website stops working. When navigating to my website I get a white screen, although this morning I got a message that the website is unsafe and I could proceed (in the meantime I did not change anything). When I go my WP-admin page, I get the following message:

“Not Found
The requested URL /wp-admin was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.”

Thus, I cannot fix the link in WP-admin. Does anyone have experience with this, or know an alternative way to go to my website settings to change the link?

Thank you very much.
Best regards,
Sanne

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