A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Put your code in Personal.xlsb to solve this issue. In this case, your function would be available to you in all Excel workbooks on your computer. (But it won't be available to anybody else. If this needs to be available to everybody else, then you will need to copy code in that Excel workbook itself).
Please refer to following article and go to the section "Making Your Custom Functions Available Anywhere"