I accidentally learned the wrong IR command into my Harmony remote and I would like to delete it

The Logitech Harmony remote software does not allow you to delete a learned command. However, if you have accidentally learned the wrong IR command, you can overwrite the existing command by learning the command again. For more information on learning a command please see Knowledge Base article 360023387833 - How to learn a command from your original remote to the Harmony remote

You can also remove the command from appearing when you access device mode on your Harmony remote:

Launch the Harmony remote control software and login to your account
From the Harmony homepage, click on the (Devices) tab
Beside the device you would like to customize, click on the (Settings) button
On the Device Options page, select Customize Buttons and click on the (Next) button
Click on the (Additional Buttons) tab at the top of the page
Locate the command you wish to remove and remove the command by clicking the trash can icon beside it. In this example we will remove "Wrong Command"
After making any changes, ensure that you click on the (Done) button to save your changes
The last step is to update your remote. Connect the Harmony remote to your computer's USB cable and click on the (Update Remote) button on the Harmony homepage