We can not put time go backwards , but we can put a clock in reverse.

Step 1: Let's Get Starting...

For this job you will need:
1- A clock with a quartz movement. I've choosen this one because it has no numeric marks.
2- A screwdriver
3- A cutting pliers
Disassemble the body of the watch to get access to the movement and the hands.
As this varies from clock to clock Ieave this step for you...

Step 2: Remove the Hands and the Movement

With careful and with the help of the screwdriver remove the hands of the face of the watch. Then remove the movement from the face of the clock.

Step 3: Disassamble the Movement

Again with the screwdriver carefully pry both sides of the lid of the movement.
Remove all the cogs in the top part of the movement. Then carefully remove the electric part. Be as careful as you can. The wires of the electromagnet are very thin and fragile. A false move and the movement turns in to trash!

Step 4: The Reverse Operation

Remove the metallic part of the electromagnet and reverse it. This is the step that makes all work as we invert the polarity of the electromagnet. You may notice some holes in the metallic part of the electromagnet. These matches some pegs in the mechanism. As you reassemble the movement you may have to cut this pegs out. (In both cases I tried before I always had to cut some pegs.