I really like the Phosphor icons. They have a clean, modern look, a great variety, and they’re free and open source. Here are my suggestions for the icons that could work well for each section:

• Splits/Plans: map-trifold (or other bullseye/target/map/route icon)
• Workout Days: calendar (or other calendar icon)
• Exercises: barbell (pretty self explanatory)

It’s not super original, but it’s easy to get.

Thank you for the suggestion. I was looking for something similar too.

More importantly, if you’re not planning to label every icon, at least add a clear heading or a tooltip that appears when you long-press a button. That way, users can tell what section they’re in or what each button does. It’s just bad UX to make people tap something just to figure out what it does.