Since the Iranian "revolution" in 1979, presidential elections have held very little significance, as ultimate power lies with the Supreme Leader. This was true under Iran's first Supreme Leader, Ali Khomeini, and remains true under his successor Ali Khamenei.
In practice, the Iranian president is merely the head of the executive branch, which is primarily concerned with the economy and managing internal power estruggles between reformists and conservatives.
This is the context that frames the death of President Ebrahim Raisi (along with Foreign Minister Hossein Amir-Abdollahian and other officials). Since news of the president’s helicopter crash broke, Khamenei immediately addressed the Iranian public, assuring them that the country's affairs would not be affected.
The Guardian Council announced that First Vice President Mohammad Mokhber would succeed Raisi and a committee comprising Mokhber, the Speaker of Parliament, and the head of the judiciary was tasked with holding new elections in 50 days. Meanwhile, the government stated that "Raisi’s path will continue."
All indications suggest that the transition of power will be smooth. The nation is in mourning, and there is significant regional sympathy following the tragic deaths of the president, foreign minister, and other senior officials in the helicopter crash.