Well, first of all, are you sure it's just your tendons? Did you contact your doctor? In some countries this is expensive, but the wrist tendons are very important and are involved in everything from typing to opening door to playing games. For this reason, you should take a hand injury seriously because although it is not as serious as another condition might be, your hand and wrist are vital to you daily life.

If it is in fact your tendon, there is nothing that you can do but use it less and wait for to be repaired. It might be worth getting a wrist bandage that will allow you to keep it straight and stiff, this way you can continue to do things with it. (Although rest is the preferred action). You could wrap it with something like a thermacare wrap, a chemically heated wrap which will make it feel cold, equally, you could use good pain relieving gel or roll on.