Create a string manipluation that replaces the 4th the last space with the expression xxx

Hi Everyone.

I tried to create a string manipulation for knime that replace the 4th last space of my string with the expression “xxx” however it didn’t work.

Do you have a solution for this or an idea what I did wrong?

regexReplace($column1$, “(.?\s)(?:(?:.?\s){3})(.*)”, “$1 x xx $2”)

many thanks in advance

Miriam