you can not, but you can delete the answer and answer it yourself.
This question has already been answered.
You can ask a question and answer your own question. You can then ask another question. If you ask a question that has already been answered you will see that in the asking process.
This question has already been answered here:How_do_you_pass_neody_in_other_age
this question has already been answered but first you have to spell CAROTID BRUITS correctly
Yes, feel free.
This question has been already answered and is in Relevant answers.
This question has already been answered once. See link.
This question has already been answered.
this question has already been answered but first you have to spell CAROTID BRUITS correctly
This question has already been answered elsewhere - see related link.
You already answered your question when you asked it so I'm not needed to tell the answer since it has alredy been answered.
When you have typed your question, once you hit the submit button, the system checks to see if that question already exists (and has possibly already been answered). If it does, it will usually tell you.