I had hardware miners that i converted to primes , never had that button
bought primes as well never had that and i have been there for a long time
As I recall, you had to click on the little settings button for each miner (the thingy that allows you to rename, merge, split, etc.) and the option to have GAW buy back your miners was there. It was only active for a limited period of time.
The option to reverse the buyback was supposed to be active for a few days only, but GAW kept it open. If you did not take advantage of the buyback there would be nothing to reverse!