This is a pretty simple tweak to either show or hide the Flow button on the entity Forms’ Ribbon.
Flow Button Not Visible
Navigate to Settings > Administration. Go to System Settings
In System Settings, under Customization tab, look for Enable Microsoft Flow option.
You’ll be asked for permission
Now, this is turned on
Flow Button Visible
Now, once you have enabled this setting, you’ll be able to see the Flow button on the View and Form ribbons across Dynamics 365 CE
That was quick!!