First extract (e.g. by using a regular expression) the value, unit and scale, then calculate the correct „final value“ by multiplying value and scale and return a string with „value unit“. Take care that the unit is correctly formatted.
As I said: Use the Javascript transformation and a regex in that, not the regex transformation. Something like
let value = /strValue="([\d,]+)"/.exec(input)[1].replace(",", ".");
let scale = /scaleFactor="(\d+)"/.exec(input)[1];
let unit = /unit="(.*?)"/.exec(input)[1];
return value/scale + " " + unit;