How do I level up my Acquaintances?

I finally got the card. I have been aggressively discarding cards trying to find it.

I think I do remember seeing this card once before…many, many months ago, before I found any Acquaintances.

I increased my Regretful Soldier from 1 to 1.5. I need him to be at 5 to be any use to me for resting/wounds.

I think the “standard” frequency is really broken here.