Call to undefined method, associate method

Hello, when I use associate, I get this error

BadMethodCallException
Call to undefined method Illuminate\Database\Eloquent\Relations\HasOne::associate()

Controller

/**
     * Create new user.
     * @param $request
     */
    public function createUser($request)
    {
        try {

            $user = $this->user->fill([
                'name' => $request->name,
                'email' => $request->email,
                'phone_number' => $request->phone_number,
                'accept_term' => $request->accept_term,
                'password' => Hash::make($request->password),
            ]);

            $address = $this->address->fill([
                'street' => $request->street,
                'number' => $request->number,
                'zip_code' => $request->zip_code,
            ]);

                $user->address()->associate($address);
                $user->save();

            return $user;
            
        } catch (\RuntimeException $exception) {
            return ['error' => $exception->getMessage()];
        }
    }

Model User

public function address()
    {
        return $this->hasOne('App\Entities\Address');
    }

Model Address

public function user()
    {
        return $this->belongsTo('App\Entities\User');
    }