Webform help

Hello,

I'm trying to set up a webform that would have two participants. This first participant would fill out and sign the relevant parts of the document. Once they have done this they will then assign the next participant who will then complete the relevant sections of the document. Once the second participant has completed the document it would be sent to me to review. 

A similar process is shown in this video - (link) The video shows that this can be done but in my version when I am adding participants to my webform I am required to add the email address of the second participant but I won't know the email of the second participant. Has anyone else been able to achieve this other than in the video?

Thanks