Apple ID consolidation

Basically, you can't, though it depends on what contents you are talking about. You could download your contents and export your calendars, for example, and also download documents, and then move them to a new ID. However you can't transfer purchases to another ID, nor move the emails addresses,

You can try setting up Family Sharing between the IDs if you want to be able to share purchases made with the IDs.

Family Sharing

Family Sharing - Set up

Family Sharing - Use your own Apple ID for Family Sharing

Family Sharing -What types of content can I share?

Family Sharing - If you don‘t see your family‘s shared content

Family Sharing - purchases and payments

Family Sharing - Hide and unhide music, movies, TV shows, audiobooks, and books