Rental property depreciation when changing from room rental to whole house rental

Hi.  My situation is that I purchased my home in 2015 as a primary residence, began renting out a private bedroom and bath in Jan 2018, and moved away and began renting the entire house in Sep 2019.  I am confused as to how to claim depreciation in my circumstance.

 

I understand that the value I'll use is purchase in 2015 and that I'd "place the property into service" in Jan 2018, but what I don't know is how to calculate depreciation, accounting for the change in how I rent the property.  Would I calculate the overall percentage use for each year?  Or do I have to create two separate properties (one for the room rental and one for the whole house)?  I also did not claim depreciation in 2018 (just realized that I could have done that), so I'll need to amend that return as well.  

 

Any help would be appreciated.  I haven't been able to find a good resource that explains my specific circumstance.