fix distorted round

[Ofnuts]

Not that hard manually, at least for such a dial where you have markings at 90° angles.

1. Start the perspective tool (Clipping: Adjust)
   
2. Adjust the handles so that the 4 lines are tangent to the dial circle at 90° angles (ie, 3,6,9,12 hours).
   
3. Apply, this gives you a rectangle
   
4. Image>Scale image, unlink the dimensions, set one of the dimensions equal to the other
   
5. Apply. Now you clock is round
   
6. To recover the rest f the image: Image>Fit canvas to layers and crop what you don't need.
   

In your image, the axis of the hands is quite long and the perspective won"t fix his, so the perceived center of the dial (where handles intersect) isn't the center of the circle (but the bottom of the axis is indeed in the center of the dial). Not mentioning that the dial is recessed in the bezel...