I haven't woke up for Sehri It's 7:30 in the morning I woke up just now.Can I fast despite of not doing niyat at that time as I wasn't awake at that time? Please help
First of all if you fasted in Ramadan without a niyah your fast is invalid. However the hanafis deviate here from the majority and say it is allowed to delay the niyah until the time of doha in Ramadan, while the majority says the niyah must have been made before fajr time
“Whoever does not form his intention to fast before to fajr, his fasting will not be accepted.” (Bulugh al-Maram)
As for optional fasts the matter is easier (See also in Arabic islamweb #213202).
Secondly if you broke the fast because you haven't performed the niyah you have committed a sin so you should repent complete the day of fast. Note according Hanafi and Maliki school of fiqh the kafara is the same as the on for having intentional intercourse during the day of Ramadan (as stated in this hadith) applies also for those who eat on the day of Ramadan without any excuse by qiyas (see What is the difference between qiyas and istislah?).
Thirdly if you had in mind to fast that day the matter of niyah is cleared as shown in the following posts:
Can niyat (intention) be done by heart, or must it be declared verbally?
Finally some scholars allowed to make the niyah for the whole month of Ramadan and it is not necessary to repeat it again as long as one didn't interrupt his fast for a legal reason (see islamqa #22909).