Just being able to pedal faster doesn’t necessarily help. All Zwift cares about is your wattage, not the speed your trainer is reporting. If you are using a power meter, increasing the resistance on the trainer would help you get higher wattage with the gearing you have. Depending on your trainer, this might be quite easy.
With a Kickr, you could go into the wahoo fitness app and change the mode to “Level” and set it at a higher level. The resistance would be similar to going up a hill rather than down a hill, so you’d be able to get higher wattage for what ever gearing you have.
If you are just on a basic trainer, if there is any way to increase the resistance, that would help.
zPower people on a basic trainer are probably just out of luck here. There you do need to pedal faster.
Lastly, changing how realistic the hills are in settings might have an impact. I know this greatly impacts the climbs, not sure if it does the same to the descents. I believe for climbs it basically reduces the effective grade in half, but due to this, you do go slower.