You find the firmware in the download section. You could use this files, I selected the newer version according to your phone.
Downloads - R1GB001_RED49 - K790_R1GB001_MAIN_GENERIC_EV_RED49 - Top Sony Forums
Downloads - R1GB001_RED49 - K790_R1GB001_FS_APAC_RED49 - Top Sony Forums
Downloads - k790custpack - HB1-06_Gen_CDA102568_101_R8A_GENERIC_APAC - Top Sony Forums

Here you got instruction about how to use SeTool2Lite Flash your phone and How to apply or remove patch using SETool 2 Lite - Top Sony Forums

I see that you don't have access to download files. See this How to get access to Download Area? - Top Sony Forums