If you have the latest Luma3DS which is version 8.0 installed on your 3DS, then you can use its Input Redirection feature to use the standard gamepad to control your 3DS. All you need is download the required file (see the link below) and connect it to the same network as your computer. Then do this:
1. Open the Rosalina menu on 3DS by pressing L + Down + Select. 2. Choose Miscellaneous options and enable its Input Redirection.
3. Run FBI app then choose Remote Install.
4. Pick Receive URLs from the network. You will see the 3DS IP address from there.
1. Run Input Redirection app
2. Enter 3DS IP address
3. Connect the gamepad to your computer
4. Start using the gamepad on your 3DS.
Video tutorial, watch this:
Required file : https://github.com/TuxSH/InputRedirectionClient-Qt/releases