Simply add more images to the project and click Align Images in the ALIGNMENT tab or press the F6 key on your keyboard. To find weak points in your registration, you can help yourself with the Inspect Quality tool found in the ALIGNMENT tab (read more here).
There is not any component in the current project. You can continue, but it is better to create some components, so that you can follow this tutorial steps and learn how to merge components which belong together.
There is a single incomplete component in the current project. Add an additional set of images. Check images visually or using the Inspect Quality (I) tool found in the ALIGNMENT tab (or press the I key on your keyboard) and add images at the places which were not covered enough. Then click Align Images in the ALIGNMENT tab or press the F6 key on your keyboard.
You already have a component containing all images. Congratulations!
Images which could not be aligned can be registered the same way as components, either by adding control points, ground control points or by adding more images. You can also try running alignment again. RealityCapture will continue from the previous state and it will try a different strategy to register these images.