Your default localisation settings can be changed under Settings > Profile. In the Localisation settings panel, you can see a preview of how your dates and numbers will be displayed based on your selection.
If you wish to define specific localisation settings for one (or some) of your clients, see this article: https://help.lsp.expert/en/articles/722801-how-can-i-change-the-localization-settings-for-one-client-in-particular
If you wish to specifically change the way your dates and numbers are displayed in the LSP.expert interface, see this article: https://help.lsp.expert/en/articles/7041505-my-dates-and-numbers-are-not-formatted-as-expected-in-the-lsp-expert-interface-how-can-i-solve-this
If you wish to specifically change the way your dates and numbers are displayed in the documents you create using LSP.expert interface, see this article: https://help.lsp.expert/en/articles/7041526-my-dates-and-numbers-are-not-formatted-as-expected-in-my-invoices-quotes-and-purchase-orders-how-can-i-solve-this