Which version of Formativ framework are you running (See Help – About Formativ)?
Formativ 1.6 only shows modal dialog which has to be closed to continue other process including showing another dialog. In your case, you need to re-display the main dialog once the secondary dialog closed.
Formativ 2.0 allow you to build custom forms and dialogs using the dynamic visual forms designer and you can display secondary dialog while the main dialog is visible. The earlier response was based on Formativ 2 framework. See the web link below for more information about creating solution with Formativ 2:
If you are using Formativ Framework 2.0 then we highly recommend you to use the Formativ 2 Forms. See the ‘Formativ Users Guide’ for more information about creating, displaying Forms. Please do not hesitate to contact us if you have any further questions or comments.