Unlikely to have any effect on the scale they describe. The first part of the power balance of our planet is the solar radiation that is intercepted by the surface of Earth. The theoretical maximum additional power added to it by these sats is going to be equivalent to the solar radiation intercepted by their mirrors. Guess how much bigger the surface of Earth is compared to those mirrors.

One important thing to note is that the climate change is not caused by the heat we released into the atmosphere. It's due to the change in the power equilibrium of the Earth caused by the greenhouse gases we released.

If this is a legitimate concern perhaps they can launch a second set of satellites to block peak sunlight.