No need to rebuild your entire contact list, just import it from your current application and format it to your address book in OS.
In order to import your clients, you will first need to Export them from current application.
NOTE: If your iOS device is already synchronized with your Google Account Contacts, you can simply export your Contacts from Gmail.

This tutorial covers how to Export your Contacts from your iOS Device (iPhone, iPad) using iCloud.
1. Go to your iOS device “Settings” menu and tap on “iCloud”
2. Toggle the “Contacts” setting to ON. Tap “Merge” to merge your iOS contacts with your iCloud Contacts
3. Next, you will be asked to go to iCloud.com to log in with your Apple account details
4. Click on the “Contacts” icon
5. When your Address Book opens, click on the settings icon at the bottom-left of your screen and choose “Select All”
6. Then, select “Export vCard” .
7. Save the vCard file on your computer

Once you have your vCard export file, you can now Import your Contacts into MYcarnegieOS!

See this article on Importing you Contacts