ok so if I understand this correctly, you have a text value of 23,91, and you want that to be a numeric 23.91.
Since the data is text, you can use the Replace function to replace the comma with a period, like this:
dim TxtNum as string
dim Num as single
TxtNum = "23,91"
Num = Val(Replace(TxtNum,",","."))
Now Num is the numeric representation of TxtNum
So, now what happens if the value is something like 231.456,92
Well, we can do this
TxtNum = "231.456,92"
TxtNum = Replace(TxtNum,".","")
TxtNum = Replace(TxtNum,",",".")
Num = Val(TxtNum)
So, we get rid of any periods by replacing them with null characters, then we change the comma to a period and convert to a numeric value with Val.