As we can see that input fed to this amplifier is the output of final stage of a multistage amplifier and if we apply KVL to base emitter loop then

Now, It is clear that the output is less than (Vbb-Vbe1) here. But I dont understand how the DC level of previous stages goes up and how this output helps to pull the DC level downward. Please help me with the functioning of DC level shifters.