Skills of the sims

This link has cheats to lower or higher skills 
https://simscommunity.info/sims-4-cheats/#sims-4-skill-cheats

Yes I know, but the lowest I can set them there is the 1st level, and I want her to relearn them in a way (?), is that possible? And also I tried this cheat and it doesn’t work for some reason:(. I tried typing testingcheats on , and then the code, yet still nothing:/ 

Luthierising has some helpful ways of doing it in this link thread 
skill cheats not working properly | EA Forums - 8545746

one way would be to duplicate your sim, create a twin and play the new sim !? 

Level 1 is the same as 0, in terms of the game's coding. So, level 1 = 0%, no progress on a skill at all.

Do you know if this differ since I have my game in polish not in English? Because none of these solutions work:( 

I am not sure but it may be best to post your question in the Polish version of the EA forums.

Level 0 means the skill will disappear from the Skill tab (skill never tried) but I doesn't always work.

Sims4studio can edit savegame files so you can remove the skill. Make sure to do a backup before editing the file.

How do I do that? 

That's a good question. I have never duplicated any of my sims but I know you can do it in the science career or in world editor with a new save possibly.....

 Good luck.🙂