Most multimeters have a diode test function.

When I get a display I know nothing about I use the multimeter and a dark room.

The diode test puts out enough voltage and current to light a segment of a display.

The black lead is negative "voltage" and the red lead is positive.

Make a drawing of the LED's pinout and segments.

Clip one lead to one of the unknown pins, wipe the other lead across the rest of the pins.

If a segment lights mark it on the drawing, other wise reverse leads and try again.