The vaginal ring is normally removed after 21 days.
If it has been less than 7 days since you were meant to remove the ring, remove the ring as soon as possible and have your 7 day ring-free break as usual. Then inset a new ring. You will remain protected against pregnancy and there is no need to take additional precautions.
If it has been more than 7 days since you were meant to remove the ring (in other words, the ring has been inside your vagina for longer than 28 days), take the ring out as soon as you remember and insert a new ring straight away. Use condoms for the first 7 days after inserting a new ring. If you recently had unprotected sex, consider using a morning after pill.