Add black and white to only part of the video

I saw several tips on how to leave the black videos blank but I need to know how I do the effect on only part of the video I don't want it all black and white 

https://forum.blackmagicdesign.com/
https://forum.blackmagicdesign.com/viewtopic.php?f=21&t=141197
4cc0unt wrote:I saw several tips on how to leave the black videos blank but I need to know how I do the effect on only part of the video I don't want it all black and white
That's actually been improved in version 17, so that now all those options appear at once.Lychon wrote:bottom left hand side of color page you will see a "1" and a "2".