I had lunch with a friend today who has been sober for about 12 years. She, an athiest, went to AA and found it a supportive process. I asked her at the time how she could surrender to a higher power, as an athiest.
She said she had to think a lot about her atheism. While it was a "rational" philosophy that she grew up with, and had been good in many ways (especially dealing with issues of social justice etc) it hadn't helped with her alcoholism. So she tried thinking of a greater "Good" instead of God - and that helped. She has found goodness in the AA groups that help her understand and live with her illness.
Good luck, I hope you get support to help you understand it all, and I hope your health improves.