You should really post where you live. But I will assume where ever you live it's winter. From the looks of the picture you caught it in time. You didn't mention any mushy spots. I would leave it as is for at least a week to dry out,and put it back in new cactus soil with no water for at least a mo...

Hello everybody, I'm a bit concerned that I've overwatered my cactus. It's turned yellow toward the bottom and the soil has remained wet for at least a month. I took it out of its pot in order to investigate it and I've attached a picture of what it looks like. Is there any way I can save my cactus?...