There could be multiple reasons for this:
1) You might have chosen a Package for your Page for which the Form App is not available. In this case, you can see if choosing a different Package with the Form App suits you. You can change the Package for your Page from the “Packages” section of your Page Dashboard. Availability of Packages for Pages, and their features are conditional depending on the settings chosen by our site administrator.
2) It is possible that you might not have configured the Form for your Page. You can configure the Form for your Page by clicking on the “Manage Form” button in the “Apps” section of your Page Dashboard.
3) You might not have activated the Form for your Page. From the “Manage Form” section mentioned in point 2 above, you can activate the Form for your Page by using the “Activate Form” field.