Access VBA find the last occurrent of a string?

Try InstrRev instead - see here

Note the different syntax to InStr:

InstrRev(stringcheck, stringmatch[, start[, compare]])

Check this link, example code from MS

https://msdn.microsoft.com/en-us/library/t2ekk41a(v=vs.90).aspx

Dim TestString As String = "the quick brown fox jumps over the lazy dog" 
Dim TestNumber As Integer 
' Returns 32.
TestNumber = InStrRev(TestString, "the")
' Returns 1.
TestNumber = InStrRev(TestString, "the", 16)