Hi,
You have two options.
1. RELAY
Connect controller data bus on common point of relay output and pins of ur modules on NO and NC point. By switching relay, you can select device to communicate with from controller driven relay.
2. MUX/DEMUX
When you have to use more than 2 devices on UART, you can use MUX and by selecting pins of MUX, you can use those on single UART.
I hope this solves your query.
Fell free to write back if required.