I assume that you haven't got the instructions for your watch.
You can get a set of instructions from their web site (tissot.com).

At the bottom of the page there is a menu; select "warranty" and a number of alternative PDF files appear on the left.

If you can't see what you want, select "user manual" from the menu at the top and enter the details of your watch.

Choose the one that is suitable for your watch and download