How to move a new custom field into an already existing field group?

Question
How to move a new custom field into an already existing field group?

Answer

1. Please go to system management, user interface, custom field layout.
2. On the left side in the treeview, expand the entity node (project, request,...)
3. Expand 'Profile' to assign the new custom field to a section in the profile page
4. Expand 'Edit Screen' to assign the new custom field to a section in the edit page
5. Expand the the section and then select the group that should contain the new field
6. Now on the right side one of the fields displayed is a list of fields 'Display in the configurable field section'.
7. From there, drag the custom field to the field above 'Display in this group' and save the changes.