On the barracks, you have a “deployment” flag that you can set on the map.
If you click on the flag, it gives you the possibility to move it, or return to barracks.
Now in your case, I guess you didn’t use the flag to move them out of the barracks but manually by selecting them, so you first need to find the “deployment” icon. It’s located on the left side in the barracks (like when you want to change the work radius for a hunter).