Hello Ydnew01.
Thank you for using Apple Support Communities. It sounds like you're experiencing issues with the Calendar app. Specifically, you're missing your Yahoo! account on the app. We can understand how this would be an issue. Allow us to investigate this issue and assist in any way we can.
First, we would like to recommend some basic troubleshooting steps that might be able to help. You can try force quitting the Calendar app and restart your device to see if that helps. Just in case, the links below can guide you through these steps:
Close an app on your iPhone or iPod touch - Apple Support
Restart your iPhone - Apple Support
If these steps don't help with your issue. You can try to remove and re-add your Yahoo! account to your device. Additionally, installing any pending updates that are available can also help. We've listed some additional resources below:
Set up mail, contacts, and calendar accounts - Apple Support
Set up multiple calendars on iPhone - Apple Support
Update your iPhone, iPad, or iPod touch - Apple Support
We hope this information is useful. Best of luck.
