Creating a background routine and confirm doses is the quickest way to record background insulin. For help on setting up a background routine, read the How do I create a background routine? article. You can also record background doses outside of a routine whether you have a routine or not.
To record background doses outside of a background routine in 5 quick steps:
Press the + button and press 'Background'
Press 'Record now'
Enter the number of units and time of the dose
If you would like notifications of when your insulin starts to work or is finishing, set the 'Receive notifications...' selector to green
Press 'Record insulin'
That's it! The What's Ahead screen will display the insulin now active in your body along with the strength and phases of the insulin at the appropriate times for your insulin so you'll always know what insulin you have active.