Walid. input to emptiness, if the field is not filled, we cannot go to the next, how to give the opportunity to return to the foreshadowing, which is filled?

Question

JavaScript

Good time of the day.
I managed to implement that we can't move to the next field if the forerunner is not filled.
Faced a problem that if the field is filled (for example value> 2) and the user passed to a trace. there is no way to return to the previous one to correct the data, since it is already
\u003e 2. Please tell me how to give the opportunity to return to the field that is filled in to correct the data.
Link to codepen:
https://codepen.io/PolyakhAlex/pen/ERaNdB?editors=1010
Thank you!