The link below contains various 3rd step prayers. I like the one below, it's simple and direct.
Friends of Bill W. - Third Step Prayers Higher Power,
I have tried to control the uncontrollable for far too long.
I acknowledge that my life is unmanageable.
I ask for your care and guidance.
Grant me honesty, courage, humility, and serenity,
to face that which keeps me from you and others.
I give this life to you to do with as you will.