VBA doesn't have an inbuilt function to find the next working day / previous working day.
You can use below code to find the next working day in VBA.
Function GetNextWorkingDay(InptDate As Date)
GetNextWorkingDay = InptDate + IIf(Weekday(InptDate) > 5, 9 - Weekday(InptDate), 1)
Note : Alternatively You can use the Workday function in Excel if you are using a higher version of Excel as explained in below link. But if you are creating a product which is going to be used in multiple versions of Excel, you should use above code.