Cookie Domain Already Defined Error

We are in the process of migrating and are troubleshooting a few issues. What should we do about the following error?

Notice: Constant COOKIE_DOMAIN already defined in /var/www/vhosts/ on line 34 Notice: get_current_site_name is deprecated since version 3.9! Use get_current_site() instead. in /var/www/vhosts/ on line 3206

As always thanks for your expertise and insight.