A super simple easy way to create a place to host a webinar is to create a FB "EVENT" and you can do that within your FB challenge group. Then in the "details" of the event you can put the date and time and zoom link.
You can make it private to members or you can open it up to the public. This way previous leads can get warmed up too.
This is an easy way to INCREASE AWARENESS of your webinar too and you can add people to your FB group.