Class B Push-Pull Amplifier
Your question sounds like homework, so I will answer in rather general terms, to give you a guide.

To find the equivalent circuit, you must operate in the conventional manner, to determine the small signal model. Power supply nodes, correspond to GND for the signal, while for simplicity, you can assume at first that capacitors have negligible impedance (short-circuit).

Then, the input impedance \$z_{in}\$, according to the proposed circuit is the impedance that "sees" the signal source in this case is composed of resistors R1, R2, R3, R4 and \$h_{ic}\$ resistance equivalent of each transistor (note that the output is emmiter). You must read about BJT h-parameters model.

In the output circuit, the current source \$i_c\$ corresponds to the current flowing through the collectors. The \$r_e^\prime\$ impedance is the impedance on the emmiter circuit, reflected to the output circuit.