You cannot do this.
A delete feature has been requested and requested again (with status-planned given about 3.5 years ago).
Register your desire for this by immediately upvoting these posts:
Deleting an application key?
How to delete an OAuth (2.0) API key?
(Theoretically, if those feature requests get enough upvotes, they might get some developer love.)...
You can see your apps, that you registered with the registration page, by going to:
This page is different for every user and you will be forced to log-in to see it.
The only place I have ever found this link is in a sidebar on Stack App's home page:
The OAuth Domain is either:
A valid domain that you own and control, and that is hosted somewhere the client can reach. Say, for example that you owned unicorns.mil.
See this answer and this answer for more information on how to configure the app registration settings. (This is "Explicit" or server-side OAuth)
Use stackexchange.com. This is a ...
Stack Exchange API Authentication
Looking for a beginner's tutorial to using the API
Yeah the registration form now says, "Website URL is required".
So, if you don't have your own website:
Enter stackexchange.com as the Application Website.
Enter stackexchange.com as the OAuth Domain.
This will allow you to use https://stackexchange.com/...
Not only is that possible, but we do it all the time.
No one can see the apps you register at stackapps.com/apps/oauth/register except you (and the SE devs).
If you don't need OAuth, then you can enter just about any fake information in the required fields.
This still allows you to use the key to get 10K quota.
It is only when you want to access ...
You're right, this is not very well documented. OAuth Domain is the domain of the URL where users are redirected after authenticating themselves.
You specify this URL in redirect_uri parameter of your authentication query. The doc says:
redirect_uri - must be under an apps registered domain
The user is redirected to redirect_uri, with these ...