From Google AI answer for "arizona aca open enrollment period":
"The Affordable Care Act (ACA) open enrollment period in Arizona for 2025 is November 1, 2024 through January 15, 2025.
What can you do during open enrollment?
Enroll in an ACA plan, Change your current plan, and Cancel your plan.
When does coverage begin?
If you enroll by December 15, 2024, your coverage will begin on January 1, 2025
If you enroll by January 15, 2025, your coverage will begin on February 1, 2025"
So it sounds like you can switch plans but coverage wouldn't start until February. You might talk to the insurance company you already paid to see if they'd refund your January premium. I doubt they would since they've been covering you for 8 days, but they might. You also might want to keep the January coverage with the first insurance company since switching and canceling might leave you uninsured for the remainder of January.