How do I Adjust Input levels in GarageBand

I am attempting to covert some audio for a friend. It is on a cassette tape and I have an old tape player (high end) that I have hard wired to the input on my MBP. I am trying to use Garageband to bring the audio into my MBP so I can burn it to a disc for her. The tape deck has a set audio output so I am trying to figure out how to change the levels of the audio coming into my MBP because they are off the scale. Are there ways of changing the input levels when importing to Garageband?

Thanks!

Barry