Here is a list of steps you can take to disable the touchpad on your laptop when using an external mouse:

1. Check your laptop’s user manual or product support page for specific instructions.
2. Adjust your laptop's touchpad settings in the Control Panel.
3. Go to Devices in the Windows 10 Settings menu. Under Related Settings, select Additional Mouse Settings and disable the touchpad from the resulting window.
4. Use third-party software to turn off the touchpad.
5. Disable your laptop's touchpad entirely.