Sure,
Answer:
He said to her if he was really that easy to forget.
-> the sentence involved in this direct speech is a question. "he said to her" does not need to be changed. sentence structure of the question needs to be changed, not like your usual indirect speech sentences.
then, add a if after "he said to her". remember, this is a question.
the word in the sentence, "was" is not a modal verb, therefore it will not be changed. however, of course the word place needs to be switched with the pronoun "he", as we're converting it to a sentence and not a question. so, "if he was really that easy to forget".