Go to https://www.freemaptools.com/find-zip-codes-inside-radius.htm and define your desired radius in miles as step 1. Then enter your ZIP code in box as Step 2. Next click the “Draw Radius” button. Then hold down as you scroll down to the “Combined” area and copy all of the data in that box. Open a new Excel worksheet into which you add the copied data. Then highlight your data and use “Text to Column” function to split ZIP codes into their own column.