@wonka1234 can you provide an example of how your string looks like?
The simplest way would be Right([your string field],4) that will get you the 4 last characters.
If you want those to be digits, you can use a RegEx tool set to parse the string with the following expression
.*(\d{4})
The formula =RIGHT(A2,LEN(A2)-4) in cell B2 is used for removing the last 4 digits of numbers in the product code.