There is no depth of field preview button on the 1200D camera. If you don't see depth of field in "Live View" mode, then it is not available to you.
If you are shooting macro shots, then the depth of field can seem to become somewhat compressed. If you want to increase the depth of field, then increase the apeture setting to f/8, or higher, and use a lot of light.
I use depth of field preview EOS T5 1200D often.. press Menu button navagate to wrench 3 icon tab to set
Custom Functions (C.Fn) #9 change to C.Fn 4: Operation/Others (Assign Set button) #4: Depth-of-field preview
Depth of field preview will than work in both Viewfinder and Live screen view when the "Set" button depressed.