Hello, microfiber cloth is really very important and useful in cleaning eyeglasses. And in fact, it's also very easy to clean microfiber cloth itself, you just need to pay attention to some details.
First, you should wash the cloth in warm water, and just use one or two drops of mild liquid dish soap or liquid laundry detergent is enough, make sure not use more. And pay attention to that do not use bleach to clean the cloth, since it will corrode the fibers.
Second, rinse the cloth and remove all the soap from it, never make any left on the cloth.
You probably don't want to wash the cloth by hand, using washing machine is still okay, but make sure you use gentle cycle.
Finally, put the cloth in the dryer, and make sure you use low setting. Or you can use air dry. That's it for how you can get the cloth clean.
Microfiber cloths are light and easy to clean and reuse, and good for attracting dirt and lint. But you need to clean them after using for a certain period. In order to clean microfiber cloths, you have to wash them separately. Firstly, you need to add some laundry soap into the water, and swish it to make suds. Pretreat stained cloths with stain remover, and let them sit for a while. And dunk and soak them for a bit. After that, wring the soapy water through them. Rinse the cloths thoroughly in cold, running water. Hang microfiber cloths to air dry completely before putting them away.
Well, it seems that your microfiber cloth really needs washed. Maybe after a long time of use, it would stink. So, it would be wise for you to have to washed with something like soap, or washing powder. In the meantime, the cloth would be much more clean and safe if you add some disinfectious water to wash it. So that there would be no chances for bacteria to grow.