App store is asking me to sign in with my old AccountID I'm working on macOS 10.13.4. When I open the App Store and attempt to update my apps which need updating, I am prompted to sign in to my apple account. However, it's prompting me to sign into foo@yahoo.com without giving me the option of changing that ID.

About a year ago, I modified my account to use a different email address, foo@gmail.com. It's the same account - just with an updated ID. How can I modify the ID within the app store?
If you have originally downloaded the apps while logged in with your old Apple ID, than to update it will ask old Apple ID and password. To fix this issue, delete the installed app, login with your current Apple ID and download the app again. This would solve the problem.