Transfer site from subdirec to root folder

I built new site in a subdirec folder and have the old site in the root dic (public_html)
What are the steps to transfer the new site to the root directory? The

My web host tried to move all the files under the dev directory to the public_html directory and changed the site url in wordpress admin, general settings but due to some reason, the site url change did not get saved and broke the site.

Please send your expert advice so I can attempt to do
it myself.

Thank you
Herman