Answer
For a previous applicant, it is not possible to book an immigration filing appointment online in advance: you need to travel to Uruguay and book the appointment in person. Certain preparatory steps may be possible before entering the country, but they do not constitute the start of the case.
Before the trip, it makes sense to gather civil-status records, apostilles, translations, certificates, digital copies, and information for the application form. However, creating an account, looking for an appointment date, or uploading files should not replace the requirement to appear in person if this is required when filing the application.
Once the appointment is booked, it is important to keep the confirmation, address, service, time, and application number, if one is issued. Booking an appointment and the official acceptance of an application are different things: the legal stage begins only when the competent authority has actually accepted the case for consideration.