Transfer to a New Host ; Same Domain Name

It shouldn’t be your host that installs it – it is you ??

Have backups of your old install, which means 2 (two) things!!!
1. WP files
2. Database
The database is the MOST important, everything is in there: your content (posts, pages, comments AND settings!)
From the files, nothing really is important – except your customized theme files (if any) and the wp-config.
However, even the wp-config has to be changed to reflect the info referring to your new database.
I assume the 4 pieces of info needed in the wp-config file (db name, db user, pw, host) will NOT be the same as on the old host.

Thanks for your reply. My previous hosting company came with WP already installed on the site. I have installed it at the new location. And as expected, my database content was gone. Good thing it was backed up ??

When you make a new install – it has an empty database. Nothing is gone.
AFTER that you restore the backed up db content.

If you proceed the other way around (1. restore; 2. install) of course, it will over-write the existing database ??

Common sense…

Sorry, I should have said “empty” instead of “gone”. Thanks again for your help.

Please consider reviewing your procedures:
https://codex.www.ads-software.com/Backing_Up_Your_Database
https://codex.www.ads-software.com/Restoring_Your_Database_From_Backup

More info:
https://codex.www.ads-software.com/Moving_WordPress

when transferring to a new host (but same domain), will my site be unavailable? and if so, for how long?

probably. depends on how fast your domain name propagates.