If you got two males, take one of them back to the store or buy another tank.
If one is a female,
#1) Remove the male from the tank (Just for a little while, so any small non-soaped container will do)
#2) Re-arrange all the plants.
#3) Do a 25% water change.
#4) Put the female back in. Wait about 20 mins for her to get situated.
#5) Re-introduce the male. The tank will look different and "taste" different, so he won't recognize it as "his territory" and won't be as aggresive towards her.
And if you didn't know, male Dwarf Gouramis are colorful, female Dwarf Gouramis are a silvery color.