Hi, i have watched tons of videos on this subject now on Youtube and they all mostly tell the same story. But they never say how we even know today that this is what happen, who wrote the story down and what is the source of it? If the Library of Alexandria burned down then how did the book survive where Era told hes work? I find myself asking myself more questions when hearing about hes work! I am not doubting hes work, i just wanna know how WE know today about the work he did! Is it a book that the Vatican took care of in their library?
As you've realised, not many of Eratosthenes' works have survived intact -- the only one is a piece about the constellations and their mythological counterparts, the Catasterisms, and even that isn't in its original form.
For the rest we rely on 'fragments', which in Eratosthenes' case means second-hand reports in sources that survive in a more intact state. There are several editions which gather these isolated reports from all over so that you can see all of them in one place. Here are most of the major ones:
Pownall's edition of On chronographies, and Roller's of the Geography, are the only ones where you should expect to find anything in English.