How to normalize data

Hello,

An account number should consist of 7 digits. Sheet 1-When the data was downloaded from an application any account that contains a zero in front of the number then it would drop the zero and becomes an 6 digits account (note: not all accounts have a zero in front). How can I normalize this so that when I try to reference/lookup to the correct account number it would know to match.

TIA for your efforts.