A serious injury like a knocked-out tooth should be promptly assessed/treated by a dentist. Carefully rinse the tooth to remove any dirt and place the clean tooth in your mouth between your check and gum or under your tongue. If you cannot do so, wrap the tooth in a clean cloth and immerse in milk. Successful re-implantation can be possible in the right circumstances if the treatment is performed promptly, so get to your dentist as soon as possible.