I had this problem one time and this is how I solved it : you have to download MCC and activate it with a computer in game (I don’t remember which settings to turn on,but you can easily find it on youtube). Then, use the code « testingcheats true », right click on your sim, and click « remove trait ». Choose the unwanted trait and voilà !
Your sim won’t have these traits anymore however your sim still suffer from moodlet linked to traits (ex= being embarassed when an active sims don’t do sport for too long) so the problem isn’t 100% solved...
The best option is to make a twin of the sim... (as far as I know)