Ron went back to time, literally

After the 2nd Battle of Hogwarts, which result death of Lord Voldermort, but also the death of many Ron friends and family, including Harry and Hermione. Before Harry last dying breath, he willed his invisible cloak, Elder Wand and the Snitch to both of his friend or whoever is alive. So Ron did what he have to do, become Master of Death to bring back the dead or prevent them.