ALL AMENDED RETURNS MUST BE MAILED .... return to credit karma to complete the amended return for free then print, ink sign and MAIL in the form.
Per Credit Karma:
Unfortunately, you can't e-file an amended tax return. ... For example, if you filed your original return using the free Credit Karma Tax® filing service, you can use it to fill out the amended return. Then you'll need to print and mail the form since it can't be submitted online
