Praise be to Allah.
1-If you woke up at the time of Fajr, then were overtaken by sleep, but you had the intention of waking up after a short while, before the time for the prayer was over, but you did not wake until the time was over – then get up and do the prayer straight away, and be determined to get up in the future. Do not let the Shaytaan play with you. We ask Allah to forgive you.
2-But if you had the intention of not doing the prayer until after the time was over, or you were hesitant about the matter – this is the action which, according to some of the scholars, makes a person a kaafir. If this applies in your case, then repent to Allah from now, and resolve not to do it again. Pray the prayers that you have missed if you know how many they are. Allah will accept the repentance of those who repent. This will be the expiation (kafaarah) for you. The same applies to ‘Asr prayer as applies to the morning prayer.