If I don’t have sufficient time for reply ASMT 10 that time is given by the department, how can I take extension on it.

An application for extension has to be uploaded in reply section. on the GST portal, one can go the "View Notices and Orders/Additional Notices" section and click on case details. Further "Reply" option will be shown where one can upload application for extension of time. The officer after considering the application shall extend the date suitable and reply can be filed in such cases within extended time.