How to find voltage and current of an led

What do they look like? can you post a picture?

Make a LED tester.

My meter has a diode mode. If the LED turn on voltage is below 2.00 volts the meter will measure the voltage at 1mA. A red LED might read 1.4 volts. Because some LEDs run about 3 volts a 9V battery and a limiting resistor would be better.

For current rating; you will have to guess by looking in a catalog and comparing.

Post a picture and many of us will give our opinion. (what ever that is worth)

If they are 5mm then all will be 20mA max and colour determines Vf @ 20mA where the threshold voltage , Vth say at 1 or 2 mA will be below the rated Vf at @20mA according to its quality and size of chip, but usually in the 10 to 20 Ohm range . so the rise will be 200~400mV

3mm less current
7seg LED 10~20mA
You can search under Digikey LEDs for representative Vf's

Since ALL single LEDs are rated at -5V max, using a 9V battery can be hazardous to the LED's life expectance with partial damage at -9V. Although it may not fail until 10V or more, it's not a great practice with unknowns. The polarity is usually marked with the flat edge being negative, BUT not always.

I have a little box that has dual row sockets where I can insert a dozen or more with different series R's marked by current.

White, Blue and Green LED's are > 3V up to 3.8V on really old poor quality ones, but typically 3.2V for nominal.

HB Red and Yellow are 2.0 ~2.2V
and deep Red old GaAs RED are 1.2~1.6V

IR LED's are 1.0 ~1.2 and invisible with a faint red glow