Start from wherever the titles are:
- In the library, select the titles and choose Merge.
- On a title's page, select Add to merge and pick the library entry to merge it into.
- In Browse or a feed, press and hold a title and choose Merge into library...
Katari then lists the titles in the order the merged entry will show them. The one marked Root is the title the others join. Drag them into the order you want and select Merge.