Helli Iszliu! You have to have a github.com account and get your github username and go under your account settings for unreal engine and go to connected accounts on the left and under github enter your github username! If you have any more questions please let me know!!
By the way forgot to mention, Their Unreal Engine github repository is private which means they choose who gets to access it. So thats why you have to connect the two accounts, Both github and unreal engine 4 account together, Then you should be able to access the page, You can see if the repo is private by looking at the top left of the page and it will have a mark “Private” next to the company and repo name, (EpicGames/UnrealEngine)