It is important to continue to learn as you transition into a new role. If you are going to be using Excel a lot you will want to review basic formulas and their functionality. As for your current issue you have actually answered it already. You need an IF statement that checks if something is a number and then if it is not a number do a different calculation.

Try the following formula and fill down.
The ISNUMBER formula returns true or false. If an item is a number it will return true. Now there is a difference to an actual number and numeric. You can remove the + 0 and see if those are the results you are looking for.

Let us know how it works.

Thanks