Your account is not enabled for Microsoft Forms Error

In Admin Center admin can search for your user or find it in Users menu, click on a user and in side panel go to Licenses (don't remember exact wording now), then expand the license assigned to a user (say E1 or E3) and then one can toggle individual apps and services on and off. Press Save at the bottom after making changes.

If Forms is not in this list, then maybe Forms needs to be enabled for the tenant, but i think you wouldn't get to that error if it wasn't enabled already and it should be enabled for all as Forms is out of preview stage. But you can still check in Settings > Services & add-ins > Microsoft Forms.

Or maybe your license doesn't include Forms. What license/plan do you have?