If the transistor is PNP, keep a good NPN in place. If it is NPN, keep a good one in the corresponding place. If both are good, the LED will flash. The frequency is given by the capacitor.

If the transistor is PNP, keep a good NPN in place. If it is NPN, keep a good one in the corresponding place. If both are good, the LED will flash. The frequency is given by the capacitor.