Wordpress | How to remove pop-up ad that goes from default wordpress kernel without free themes

I have just downloaded wordpress from wordpress.org and installed it on my hosting. Then when my site has already saved and published, when I open it from another phone and computer I get the pop-up advertisement in top-right corner. I created the site without any free themes that might have ads. I use wordpress 5.2.3. ...So if someone had that problem too, please response. I need the site immediately. I have never seen this problem before and on whole internet no answers about it.