Where do I adjust forward voltage on LED
Like any diode, the relationship between current and voltage in an LED is not linear, then it is common that the manufacturer specifies a certain voltage at a certain current, in tabular form, or by means of a graph.
In the real circuit, the design parameter is the required brightness. With this value, the current required is determined. The voltage drop over the diode is set based on the current level.
For an ordinary LED, 10 mA is a normal operating current.