This table shows max. ratings only. Usually you'd find diagrams showing the I vs. V characteristics in the datasheet, to. From these you take the voltage drop at a given current.

There is also two values for current (peak and constant), and I am not sure which value to use in my formula.

As it says: "continuous forward current" - that is the current you can drive savely through the LEd for prolonged periods. If you were to pulse (blink) the LED, you should also find a graph showing pulse current vs. duty cycle in the datasheet.

If you don't have the datasheet with curves, you can measure the voltage drop at a given current using a power supply with variable current limit: Set the current limit to e.g. 30 mA and measure the voltage drop across the LED.

You don't have such a power supply? experiment with e.g. a 9 V battery and different resistors to approximate a current f 30 mA, then measure the voltage drop across the LED. As a starting point you may use the

table shown here to approximate the expected voltage drop for use in your equation for the resistor.