In the 1930s, one of the original "squats and milk" plans was 2-3 days a week of squat, pullover, behind the neck press, and barbell curl. Go lol that.
On topic, see pic.
EDIT: Pulled from your thread last month:
^ This, plus this thread being the third time you're trying to add something to the program (first was dips, then something "to target the vastus lateralis", now curls), tells us that you're losing focus of the big picture. (pun intended)
You need time and calories and consistency. You're barely 140 pounds. Focus on getting closer to 160+ while building total body strength and see if you need to worry about "starting biceps development."