Here is U.K. I have a brother who has exam on the same date it’s eid and the timing clash. They are one of final exams. What can one do? If missing eid namaz will his Ramadan be accepted as school won’t let him be late as it’s final exam.
Eid prayer is an optional prayer he may do it or leave it.
Note that he even can pray it later (alone) as qada'. I've read that some scholars accept it even one day later others say it must be performed before noon of the Eid day.
Praying Eid or leaving it has no impact on the validity of fast or the acceptance of it. What is necessary to complete the fast is to pay the zakat al-fitr or sadqah of fitr. This a mandatory act on each Muslim, each Muslim must pay it for each person he is in charge of unless he can't afford to survive that day if paying it. And it must be paid or at least leave his hands before the Imam starts the prayer! One could pay it during Ramadan however delaying it until the night before the Eid is the most recommended.
He may do it the next day at a similar time.
Eid Prayer is a Fardh prayer (obligatory), according to Salafis, while according to Hanafis, it is a Wajib (nessecary) prayer.