Watch pins hold the links of a watch bracelet together. Only the three or four links on each size of the clasp have pins that can be removed. If you want to resize your Tissot watch band, you'll need to remove pins to either remove a link (making the band smaller) or add a link (making it larger).
Place your Tissot watch on a soft cloth to prevent it from getting scratched while you are removing the pin.
Turn the Tissot on its side so the links are vertical. On the inside of the links around the clasp, you will see arrows. These arrows point in the direction that the pins must be pushed out. On the edge of the link closest to the base of the arrows, you will see a tiny circle where the pin is inserted.
Place your pointed tool on the tiny circle and push down on the pin in the direction the arrow is pointing. You may need to use force, but be careful not to scratch the watch band. You can use a pointed tool from a hobby or jeweller's kit, or you can use a thumb tack. Push the pin out with the tool, then pull the pin out completely.