Need to change siteurl value

I need to change the value of siteurl so that my clients domain is displayed in password emails, instead of mine. My client has used a frame redirect to my domain.

I’ve tried changing the following to my clients domain:

a)define(‘WP_HOME’,’https://example.com’);
define(‘WP_SITEURL’,’https://example.com’);

b) Changing value of siteurl in database.

Both of these did not produce the expected result. If I cahnge the value of siteurl then the site cannot be accessed.

I need help with the site_url function so that I get the same domain that the user does not see my domain name in their emails.