please help i need logic pro x for mid 2009 mac pro el capitan 10.11.6

hey , i don't understand . i got this macbook for fathers day as a gift from my sons , and it had Catalina on it ,i was trying to use a audio interface for a home studio , and tried everything ,but it would not show up in the output bar . so i bought this hard drive with el capitan 10.11.6 , thinking it would solve the problem , which it didn't . i ended up getting a plug and play interface. now i can't get logic pro x back. And i had it with the Catalina hard drive. any ideas from where two go next

well I'm sure my boys didn't know , they were trying to gift there dad . but thank you so much for your time . GOD Bless

and they bought this mac from someone on offer up . thanks