You can use the de-register option in the portal to submit the application. Basic documents that can be asked by FTA are : 1) Undertaking letter stating reasons for de-registering; 2) Company license cancellation/termination letter if the company is liquidating; 3) Monthly Turnover details for the last 12 months (sometimes even from 2018 onwards); 4) Financial statements audited/management accounts for 2018 and 2019; 5) Bank statements from 2018; 6) Bank account closure letter if the company is liquidating. They may ask all or more details than the above.