Not so easy. The usual way of getting a triangle (sawtooth) wave is to charge a capacitor with a constant current and then discharge it quickly.
However, the charge rate is constant and therefore the amplitude reached will depend on for how long the charge is going on.
Since the period of your square wave depends on which note (frequency) you select, the amplitude of the triangle will get less as the frequency rises.
There will be ways around this, but it gets complicated.
Why do you want a triangle wave? It won't sound much different to a square wave.