The description displayed in the Google results can be updated by clicking on the page name, under the website creation tool, and then on ☰ and SEO (in the toolbar, at the bottom left of the orange panel). You'll then be able to modify the page title, Url, description and keywords. In general, this description will be displayed on Google, unless it doesn't contain any of the keywords, in which case some sentences of your page will be displayed. Run your mouse over each area to get more information.
Please note that it will generally take several weeks for the changes to be taken into account by Google.