1. Login to Self serve.
2. From the Self Serve drop-down menu, select Mobile services.
3. Under “Manage your phone number,” select Manage.
4. Select Find a new number.
5. Choose the province and city for your new number.
6. Choose a new area code and the first three digits from the drop-down list, and select Next.
7. Choose a new phone number.
8. If no phone numbers appear, select a new area code number and search.
9. Select Next.
10. Review your changes and select Submit.
11. You’re done! Your new phone number will be confirmed.

https://www.koodomobile.com/en/help/changing-your-phone-number