Template extended class

Hi, i’m trying to implement an extended class that will overwrite EMailTemplate, all good with implementation the only problem i’m facing is when it tries to load, i’ve put the necessary things in nextcloud/config/config.php line
OCA\MyApp\MyClass and my app is in apps/MyApp/MyClass, and i’ve set the namespace from MyApp as OCA\MyApp , the problem i’m facing is that it doesn’t work and i dont understand why,for other namespace enviroments such as OC/(other folders) it works,but on update it is being deleted, can someone help me …? I followed the example from documentation