You can add a zero before a number in Google Sheets and Excel using this tutorial. You need to change cell formatting or use function.

One of the easiest methods to stop Excel from deleting leading zeros is to insert an apostrophe before the actual number. The number will be displayed without the apostrophe symbol.

When you type a seven-or-ten-digit phone number into an Excel cell that uses the phone number format, Excel will automatically change the way the number looks so that it appears as a phone number.