Question

Who did tell you?
[spot the error and rewrite the question]

Answer 1

${\sf{\underline{\orange{Answer:}}}}$

Who told you?

• 'Did tell' gets replaced by 'told' here.

Answer 2

Who told you ?

The sentences is in past tense. In past tense, did will not come. The past tense of the verb is used

The past tense of tell is told

So the answer is Who told you ?