Here are the steps to get your range out of demo mode:
This option is for use by retail establishments for display purposes only.
(The heating element does not operate).
How to enable or disable the demo mode
1. Press Options for 3 seconds.
2. Press or to select 0, and then press START/SET.
3. Press or to select ON or OFF.
4. Press START/SET to save the changes.
(for more info, you can turn to page 38 in your user manual- https://downloadcenter.samsung.com/content/UM/202103/20210322170107572/NE63T811_AA_DG68-01212A-04_EN... )