How do you call a relation attribute in form?

public function getFullNameAttribute()
    {
        return ucfirst($this->first_name) . ' ' . ucfirst($this->last_name);
    }

public function getFullNameAttribute()
    {
        return ucfirst($this->first_name) . ' ' . ucfirst($this->last_name);
    }

public function getFullNameAttribute()
    {
        return ucfirst($this->first_name) . ' ' . ucfirst($this->last_name);
    }

public function getFullNameAttribute()
    {
        return ucfirst($this->first_name) . ' ' . ucfirst($this->last_name);
    }

In table I just call : customer.full_name
I know it's not possible that way but can't make it work.

Forms\Components\Group::make()
  ->relationship('customer')
  ->schema([
    Forms\Components\TextInput::make('full_name')->disabled(),
   ]),

Forms\Components\Group::make()
  ->relationship('customer')
  ->schema([
    Forms\Components\TextInput::make('full_name')->disabled(),
   ]),

Forms\Components\Group::make()
  ->relationship('customer')
  ->schema([
    Forms\Components\TextInput::make('full_name')->disabled(),
   ]),

Forms\Components\Group::make()
  ->relationship('customer')
  ->schema([
    Forms\Components\TextInput::make('full_name')->disabled(),
   ]),