The white space that you are seeing at the top is related to the padding for the default header area for the hello theme.
So if you added a logo within Appearance > Customize from your WordPress Dashboard and/or added a Menu Item to the Main Menu Location from Appearance> Menus > Menu Locations from your WordPress Dashboard, this header content would appear in this section.
There are two ways you may remove this white space.
Simply change the page layout to Elementor Canvas as illustrated in the doc below-
The Elementor Canvas Layout is more specifically designed to remove the header and footer locations from the page in use case scenarios for landing pages for example. You may read up more about this from the link given above.
Please note that if you decide to use the Theme Builder for Elementor to create a Header and/or Footer template to apply to your pages(s) globally, any page that has this Layout option enabled will not get the Header and Footer Templates applied to them and you will be required to change this to the Elementor Full-Width option in the future.
The second option to remove this space is to design your header and footer using the Elementor Theme Builder and then simply assign these templates to your pages globally so you would need to rebuild them on a per-page basis.
Here is an example of how you may simply copy and paste the already created header sections to the header template and assign it to your page once completed.
Hope this helps.