Combining lessons within the same course

Put the entire lesson into a Block Template. Then insert that block into another lesson. After you're sure everything transferred, delete the unneeded lesson. You can also delete the Block Template after it's been inserted.

Here's the User Guide info on Block Templates: https://access.articulate.com/support/article/Rise-Creating-Sharing-and-Reusing-Block-Templates 

BTW, you might want to create a backup copy of the entire course before you start, just in case something gets deleted accidentally.