@nanashikun I can get you pointed in the right direction. What you need to do is find a version of Android 7.1 or greater that will install to your box, the bootloader is installed during this process. A lot of people have had great success with ATVxperience or Aidan’s Rom.
@Garcea has posted links to both in another thread, quoted below:
To install these, or any other AMLogic Android firmware, you’ll need a windows utility called the AMLogic USB Burning Tool - AND a USB 2.0 A - Male to Male cable - this link as an example. Do some thorough google research on the usage of this utility ahead of time.
I would also highly recommend that you make sure that you have a copy of the default Android 6 ROM for your box in case something goes wrong, otherwise you could brick your box and have nothing to go back to scratch from. Chinagadgets reviews or XDA Forums is a good place to look for that.
This forum is also a rich source of information about updating S905x bootloaders for NG builds but the information is nested in various threads.
In the interest of not totally hijacking the intention of this particular thread, you can PM me when you have more questions. I’m more than happy to help. Good luck.