How to change from https://xxxx.com/subdomain to https://xxxx.com ?

Hi,

If I understand correctly you want to move your website from sub-domain on main domain, if is so please check those articles.
Move WordPress from Subdomain to Root ->https://askwpgirl.com/move-wordpress-subdomain-root/
How to move WordPress from subdomain to root domain -> https://hostpapasupport.com/move-wordpress-subdomain-root-domain/
Ensure that your website has been correctly and fully transferred to the new domain. Many of our users have made these transfers using the WP Duplicator plugin. For more details about that plugin, you can check here -> https://www.wpbeginner.com/wp-tutorials/how-to-move-wordpress-to-a-new-host-or-server-with-no-downtime/

Thank you!