You need to install driver before starting to use the tool.

See Driver-install-on-Windows.

0. Boot your device into Flash(Programming) mode. Usually you can start the mode by pressing button on the device.
1. On menu bar click Device -> Select, then choose your chip name. (In most cases ATmega32U2 or ATmega32U4)
2. On menu bar click Settings -> Communication -> USB, then click Open button on USB Port Connection dialog. At this point you'll have to plug into USB and start the Flash mode.
3. On menu bar click File -> Load HEX File, then select your firmware hex file on File Selector dialog.
4. On Operations Flow panel click Run button to load the firmware binary to the chip. Note that you should keep Erase, Blank Check, Program and Verify check boxes selected.
5. Re-plug USB cord or click Start Application button to restart your controller. Done.

See also FLIP instructions if needed.

First, try to remove current driver and re-install from Device Manager. See Driver-install-on-Windows#troubleshooting.

• FLIP: AtLibUsbDfu.dll not found
• Could not open USB device