Need help transferring QB for mac 2019 from old computer OS11.7 to new computer running OS 15.6

Need help transferring QB for mac 2019 from old computer OS11.7 to new computer running OS 15.6

I need help! 

I have read so many different ways to do this that I have ended up in a mind maze and I'm stuck. 

- I have my original disc and license

- I have installed QB on my new computer 

- I have the latest back up on an external drive

- I dragged the latest back up dmg file to the folder with the older back ups

- I am running the latest version of QB on my new mac

- I have not deauthorized from first computer because I am afraid 😉 I don't want to lose access to something that works

- I have worked on the older computer and would love to not have to input that data again (thus the latest backup file)

When I open qb 2019 on new computer I go to "open company" and my latest back up is greyed out. 

I think I should delete the files and program from the new computer, then download the app again? then transfer from the latest back up? Also I can't figure out where/how to enter license code. It asked me once before I located the disc. When I go to manage license, I cannot select any of the choices. 

Can someone give me a step by step to get out of the maze please?

Thank you!!!