cant find how to add a gruop when using the weight paint tool see thread

hi creating a flaaping flag with the weight paint see tutorial at bottom link

I am following this tutorial i am using the ltest version of blender . I cant find how to add the group after ive used the weight paint. When i press ctrl alt a to see the effect play. I just get the plane moving away

any help on locating this

see link

In the Cloth settings directly below the ‘Pin’ tickbox, there is the box to select a vertex group