How do I convert owner-occupied duplex to full rental for 2018?

For the past several years I have had our duplex entered as one property and let Turbotax calculate the expenses and deductions at 50% -- meaning 50% of the duplex was used as rental and 50% was used as personal residence.

We moved out-of-state and in January 2018 we rented our side the of duplex.  So for all of 2018 both sides have been fully rented.

How do I convert the side of the duplex that was personal to rental?

I have read various posts that talk about splitting the rental into two properties, but I'm not sure how to do that, or if that is even the right approach for my situation.

Under Business -> Business Income and Expenses -> Do Any of These Situations Apply to This Property?  I see the option "I converted this property from a rental to personal use in 2018"

But I didn't convert the *entire* property to rental, just 50% of it.  So I'm not sure checking this option is the correct response.

How do I correctly tell TurboTax that I want to convert the half of the duplex property that was personal to rental?