NEVER put in a microwave oven.
It will damage the card, the oven and you!
What this does is repair microfractures that can happen in PCB's over a period of time.
Heating just enough, is sufficient to melt the solder very slightly so that it can repair such fractures.
BTW - My card works fine when I use normal applications, but 3D Mark or OCCT or games dont run fully, they result in artifacts on the screen and the rig hangs up. So RMAing the card anyway.