Can I use the same serial1 port to communicate with two modules?
Yes you can. 

Detail for GPIO alternate functions are in https://www.st.com/resource/en/datasheet/stm32l432kc.pdf, chapter: Pinouts and pin description (page 55-56). All you have to do is change alternate function of gpio pins after initialization if serial port have same configuration. If configuration isnt same for both modules you also have to change it before you want to communicate to other module. You can find how to change alternate function of GPIO here: https://www.st.com/resource/en/reference_manual/dm00151940.pdf, chapter: General-purpose I/Os (page 271). 

Depending on used IDE it might be easier to De-init and Re-init used serial peripheral instead of changing registers yourself (initialization routines will change exactly same registers).