Unable to find error messages customization

Hi @montino

Thanks for writing in,

Please go to: Appearance > Theme Editor and then add the following codes on functions.php file of your theme.

add_filter( 'user_registration_response_array',function( $response_array, $form_data, $form_id ){
	if( is_array($response_array) && !empty($response_array) ) {
		foreach($response_array as $key => $message ){
			if('Password should not match with Username or Email address.' ===  $response_array[$key]){
				$response_array[$key] = __('your custom message','user-registration');
			}
}
}

I hope this helps.

Regards!
WPEverest Support Team.