If you miss Fajr because you slept through it or forgot, pray it as soon as you wake up or remember.
Make wudu (ablution), then pray the two obligatory rak‘ahs (units) of Fajr; do not deliberately delay it once you are awake. The Prophet ﷺ instructed that when a prayer is missed through sleep, it should be prayed when remembered (Sahih Bukhari, Hadith 595).
If you missed it intentionally, sincerely repent to Allah, resolve not to repeat it, and pray it immediately. Allah knows your circumstances, so do not despair—act promptly and improve your arrangements for the next prayer.