In Hanafi teaching, missed Witr must be made up as three rakats with Qunut. It is not replaced by one rakat. Arrange the timing with a teacher if Fajr is imminent, sunrise is approaching or you have other missed prayers. Make-up guidance.

If you have already prayed Witr and later wake for voluntary night prayer, you may pray without repeating Witr. The instruction to make Witr the last night prayer is a preferred arrangement, not a ban on praying later. Sunan Abi Dawud 1439 reports that Witr is not repeated in one night; its displayed grade is sahih, al-Albani.