To add new users to a training campaign in progress, you'll want to ensure the "auto-enroll" function is turned on in your training campaign, and then add those users to the console. If you've already added the users to the console, pay special attention to Step 4.
To new users to a campaign in progress, follow the steps below:
Click on Training, then Campaigns to see a list of your Training Campaigns.
Click the drop-down located towards the right of the campaign you wish to add users to, then click Edit.
On the page that follows, make sure the Automatically enroll users that are added in the future function is checked, then click Update Training campaign.
Next, consider whether the campaign you're editing has specific groups selected, or if it is assigned to All Users. Also, were the users you'd like to add to this campaign already added to the console prior to checking on the auto-enroll function?
If the campaign has specific groups selected rather than All Users, you will need to add your users to the Groups that are a part of that campaign for them to be enrolled in training.
If the users you'd like to add to the training campaign have already been added to the console (or the groups assigned to that campaign) when the auto-enroll function is turned off, you'll need to delete those users from your user list and reimport them (or remove them from the selected Groups and add them in again) upon turning on the "auto-enroll" function. The reason for this is because the auto-enroll function does NOT work retroactively.