Grab the lock with your left hand (so that opening lever points to the right.) in a way that your finger tips bring tension on the lock. You will need a high amount of tactile impressions on your fingers.
Now with your right hand rightmost finger (the small one) push that opening lever to the right, again to bring tension on the mechanism.
Then carefully twist the numbers. Start with the rightmost one. You will feel a slightly different impression when the opening slot for the correct number rolls into place. This procedure will take some time (most likely you will need 3 - 4 rotations of each wheel until you get the feel of it.
If tactile did not work place your ear close to the lock and repeat, you will hear a scratch when transitioning from a wrong to a wrong number but a more clicky sound when transitioning from a wrong to a correct number.
As a sidenote: Such locks are totally worthless if you want to prevent theft or anything like that. The only thing that they do is keep the zipper shut while its on board. See this video on how easy it is to break a zipper. The reason the locks are useless are that the zipper is so much easier to break into that nobody would bother to even try breaking that lock.