It is easy to get a reminder of the web Authentication Code of any company you are trying to register a company with Inform Direct.
At step 2 of the set up wizard where you have been asked to enter the code you have the option to click on the link "Send me my code"
Note: For companies where the import to Inform Direct has already been completed then you can request a reminder of the Authentication Code to the Registered Office here from Companies House. If you need to request the Authentication Code reminder to be sent to home address use this link here.
Once you have clicked on the link you will see this screen confirming that it has been requested:
You will see the Registered Office of the company which is where the code will be sent. It will usually arrive within 5 working days, but is often quicker.