Don't tell them what not to do unless you tell them what to do instead
They are doing it wrong because they don’t know how else to do it. They probably even know they’re doing it wrong so telling them isn’t helpful.
In the absence of any other guidance they’re just going to continue doing it the only way they know. Even if it’s the wrong way.
Tell them how to do it better – and if you don’t know how either, that’s ok: you can work it out together.