The edit symbol opens the document that has been loaded, but there is no way to actually edit it. The only way to edit the document is to edit it before uploading.
I am more than familiar with online processing, but lose patience when the system is poorly designed, does not offer suitable options for the user to input the required information, a comprehensive guide to its use or a contact facility to help those having difficulty with the system.
I have 3 German friends who have given up with it. They wanted to spend 3 months in Thailand but were asked for so much information, forms, contracts, receipts etc. from the owners of the properties they were renting and it was proving impossible to input all the information into the visa application. In the end they just cancelled their trip. They will be spending their Euros in Malaysia instead.
The Thai need for paperwork, be it hard copy or electronic, borders on the obsessive.