Dear
How Can I change Default group for New Membership FBA users so they be automatically added to a SharePoint group instead of choose a group for every approved user
If you're using the Membership Request Web Part, you can edit the web part properties and select the group that you'd like new users to be added to.
very Thanks to your help, :) it is worked
How can I create new group for FBA users .
You just create a standard SharePoint group and call it whatever you like. Site Settings -> People and Groups.