1. Check for port names pactl list sinks (I remove non needed sinks output):

   
   
   

   Sink #1
   
       State: RUNNING
   
       Name: alsa_output.pci-0000_00_1b.0.analog-stereo
   
       Description: Built-in Audio Analog Stereo
   
       Driver: module-alsa-card.c
   
   ...
   
       Ports:
   
           analog-output-speaker: Speakers (priority: 10000, not available)
   
           analog-output-headphones: Headphones (priority: 9000, available)
   
       Active Port: analog-output-headphones
   
       Formats:
   
           pcm
   
   




2. Set sink port using pactl set-sink-port:

   
   
   

    pactl set-sink-port 1 analog-output-speaker
   
   

   
   
   

   or

   
   
   

    pactl set-sink-port 1 analog-output-headphones
   
   

   
   
   

   If you are using a removable device (Example: USB devices), it's better to use sink name instead of id. For example:

   
   
   

    pactl set-sink-port alsa_output.pci-0000_00_1b.0.analog-stereo analog-output-headphones
   
   

Reference: man pactl