Add a new page from Pages -> Add New.
Click "Edit with Elementor".
Wait several seconds until the Elementor interface finish loading.
When the Elementor interface loads successfully, click Settings -> and choose Elementor Full Width on the Page Layout options.
Click Add Template button.
Then select "My Template" and pick the Platinum Template you want to use for that page.
Rename the Page Title (EG: If you intend to use the Page as Homepage, then rename it to Homepage #1).
Publish the Page (click the green Publish button).
Now to set that Page as Homepage, from WP Admin visit Settings -> Reading.
On "Your homepage displays" options, select Static Pages -> Homepage -> select the Page you just created.