"Credits received" should refer to any payment you have made to us, and this would align with the date of 31/01/2021 which would be when any liability for tax year 2019/2020 is due.
Regarding any refund you are due, you should be able to see any credit on your account shown on the "Current Position" section of the account.
There should then be an option there to claim this back, as well as another section of the account titled "Request a Repayment".
Both of these will give you the option to request a repayment via BACS transfer.
If you have further questions/wish to check the status or timescale for any repayment, then you can contact our Self-Assessment department:
Self Assessment: general enquiries