Yes, you can cancel your application providing your award payable date has not passed, or if your award payable date has passed but your award has not yet been completed.
If you have submitted a retirement benefits claim form (AW8) please ask your employer to contact as soon as you are certain that you no longer wish to retire. If you have submitted a deferred benefits claim form (AW8P) you should make your request to cancel your application in writing. Please write to:

NHS Pensions
PO Box 2269

However, If you are claiming your deferred benefits and you have already reached your normal pension age, we will be unable to cancel the application once your completed form has been received. This is because your benefits are payable from this point.

You can also contact the NHS Pensions Members helpline on 0300 330 1346 to advise of your intention to cancel your application, however you will still need to make your request formally in writing.