You can't - a single formula can only return one data type. You have both string and number, so it has to be a number.
However, if you need the number elsewhere, I would create a formula something like this:
if not IsNull({TBL_COMPANY.CUST_NODHW_1Q_082920825}) and not IsNull({TBL_COMPANY.CUST_NSHW_1Q_082741358}) then
{TBL_COMPANY.CUST_NODHW_1Q_082920825} + {TBL_COMPANY.CUST_NSHW_1Q_082741358}
else
0
To format the number in your string result, like I said in my first post, do a search in the Help for To_Text and look at the information for formatting numbers.
-Dell