You have to enter your old site URL and new site URL then just dry run and check number of links to be changed/updated. Then un-check the dry run and run the process again, it will replace all your URLs with the new one.

Hopefully, it will fix your issue.

Thanks

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

I guess you have some browser cache there that’s why you are not able to access the page.

Thanks