Check the manual and find out which pair of connections on the amp will allow you to run the amp at 1ohm safely. Some amps are weird about what works and what doesn't. Then, just run a wire from the + terminal at the amp, to the + connection on the terminal cup. Inside the box run a wire from the + side of the cup to the + hookup on the first voice coil, then run a short wire from there to the + hookup on the second voice coil. This should create a single line with all of the positives hooked together.
Do the same with the negatives, and you'll effectively have it wired in "parallel", which will leave you with a 1ohm final load, assuming you have a D2 sub.