Playdrumsonline supports all midi devices, you can connnect your midi device through web midi. The only browsers that currently supports web midi are the Google Chrome browser and Microsoft Edge browser.
To connect your midi device, connect it either through USB or Bluetooth.
Click the settings button to open the menu, here you will find the options for different input settings. Your midi devices will be listed here. If your device is not listed, make sure it's connected to your computer and currenctly not in use by another program.
You can choose to use the default input settings, wich will work in most cases. But you can also setup your own. Use the easy setup method or the advanced to control the game with different midi notes.