Received benefits but immediately returned to work. Reported overpayment to EDD but have yet to be instructed on how to repay the benefit. How do I report this?

You must report the full amount of the benefits you received on your 2020 tax return.  Assuming you repay in 2021, that repayment will go no the 2021 return that you file early next year.

Can you let me know how to report repayment in 2021? I choose standard deduction. Thank you!

If the repayment is $3000 or less, you must deduct this in Schedule A. If you claim the standard deduction expense, you will not be able to claim a right of repayment deduction if you don't have enough other deductions that are over and above the standard deduction amount.

If your repayment amount is over $3000, you can take a credit but it is a complicated process involving downloading the Turbo Tax software. Here is a link describing the step by step process for claiming this credit.