If the /etc/resolv.conf file does not retain changes on your server with Plesk, it's likely that Plesk is managing DNS settings and overwriting this file. Plesk uses its own mechanisms for DNS configuration.

To update DNS settings in Plesk, follow these steps:

1. Log in to Plesk:

   • Access the Plesk control panel using your credentials.

2. Navigate to DNS Settings:

   • Go to "Tools & Settings" > "General Settings."

3. Update DNS Servers:

   • Scroll down to the "Preferred DNS Server" and "Alternate DNS Server" fields. Enter the DNS servers you want to use.

4. Apply Changes:

   • Click on the "OK" button to save the changes.

5. Restart DNS Service (if necessary):

   • In some cases, you may need to restart the DNS service for the changes to take effect. You can do this from the Plesk interface.

If you still need to make changes directly to the /etc/resolv.conf file, you'll likely have to adjust Plesk's DNS settings or configurations so that it doesn't overwrite the file. Keep in mind that manually editing system files should be approached with caution, as it can lead to unexpected behavior.

If you're not sure about making these changes, consider seeking advice from your hosting provider or a system administrator who is familiar with your specific server setup.