Total Newbie can't merge armies

[Yasha]

I'm experimenting with Tribal Finns. When I declare war (to use three groups of 99 zealots my chaplain recruited for me), I cannot figure out how to merge them with the 600+ levies I was able to raise after declaring war. They all moved as separate groups. In another battle, an enemy invaded me, and I was never able to group the various contingents from vassals, plus my own levies, plus mercenaries, into a single army. They kept moving and fighting as separate groups, making it impossible to win a battle.

I can't find anywhere in the interface options to combine units all stacked together. How is this done?

The manual indicates that the option exists, but darned if I can find it.

Game version is the latest, with all DLC except Sunset Invasion.

[Lizardemus]

Once all armies are in the same province, highlight them and click the two inpointing arrows in the army list screen, top left.

[Yasha]

Thanks!