website not working with www but working only without www

I am looking for a developer who can fix my custom-built website so that it works with the "www" prefix. Currently, the website is only accessible without the "www" prefix.

Skills and Experience:
- Experience with IIS web servers
- Knowledge of custom-built website platforms
- Familiarity with DNS and domain configuration
- Ability to troubleshoot and fix website connectivity issues

Timeline:
- The issue needs to be fixed immediately

Please provide examples of similar projects you have worked on and your proposed solution for this issue.