Advice courtesy of “Pick it, Lick it, Stick it Campaign” championed by Kings College Hospital & Dental Trauma UK

Pick up the missing tooth by the crown, not the root
Lick it if it’s dirty
Stick it back into place
Then get to your General Dentist!
If you can’t get to your Dentist immediately, stick the tooth in milk to preserve it but you will need to see the Dentist asap.