This claim is baseless. Those who claim this false story say that Safawi ruler forced Sunni to follow Shia faith. Millions of Iranians are still Sunnis and no one forced any one to accept Shia faith. Safawis ruled over many countries including Iran, Afghanistan and parts of Indian subcontinent but history never recorded any force on any one in the matter of faith. Till today Sunnis of those areas are still Sunnis. This fact itself is a living evidence against that false claim.
Wassalam.