I answered your question with a correct answer and you told me it doesn’t work (it does) and that you now have a different question. I’m not sure how to help you…
Also “it does not work” is not enough information. It’s best if you can provide a screenshot of the blocks you used.
If you use the Replace All block, you can replace the 0 with “” (empty string) and you can replace the 5 with a 0. That solves all three of your initial questions.
For your newer questions, you’ll have to play around with the Text blocks. But I can tell you that to replace digits at various places within a single text string, you’ll need to use a [text substring] block or a loop through all characters in the string (probably also with the text substring block).