You should open the notification page and you should see a message regarding uploading your test. On the last line you will see a mention about sandbox or 5 and 7 days underlined in blue. Click that and attach the snapshot of your self-test ATK next to your passport.
In the Lab Report just fill in ATK Day 5
In the Release Date just fill in the date that you took the self-test.
Result- choose the result
Attach the snapshot and submit.