If you have a dual voice coil woofer and want to drive it with a stereo amp you simply connect one channel to each voice coil. It's the same as if you had two separate woofers.
There are other ways to do it but it depends on whether you can bridge the amp to mono, the impedance of each voice coil, and what's the minimum impedance the amp will run when in stereo or bridged (bridged is usually half that of stereo mode).