Download latest Android 6.0 stock firmware for Beelink GT1 Ultimate TV Box from here or here. Download Amlogic USB Burning Tool v18.104.22.168 from here. Here you can read about the unboxing Beelink GT1 TV Box.
Archive: Beelink GT1 ultimate OTA v311M0 AP6255 20170224
Model: Beelink GT1 Ultimate TV Box
Image file size: 368 MB
Platform: Amlogic S912
Image name: q201_9377-ota-20170224.zip
Inside archive: firmware + factory_update_param.aml + recovery.img
Build number: Amlogic/q201_9377/q201_9377:6.0.1/MHC19J/20170224:user/test-keys
Caution: Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.