Obliviate is a permanently altering someone’s memory and therefore can not be undone.
In Harry Potter and the Deathly Hallows: Part I, Hermione Granger casts Obliviate on her parents. Hermione wanted to keep her parents safe from potentially running into Voldemort by ensuring he had no reason to come a-knocking. She also promised that she would find them and reverse the magic when all was said and done.
What spell did Hermione use on her parents to temporarily erase their memories? It says Obliviate in film and unknown charm in books. Hermione SPECIFICALLY states that she MODIFIED her parent’s memories. Also, later on, in the cafe, Hermione says that she had NEVER done Obliviate before.