Not a direct translation and probably the "german" way to say this in german. If youre "there (somewhere)" again, technically youre "back" there. So the "again" is implied. "I am here again!"/"I am back!" technically can mean the same thing. Im sure there is another way in german to express the nuanced meaning of the former expression.
I am wondering if one would say "Mir ist zurück" in the same vein as "Mir ist kalt" -- where the latter suggests a temporary change in status (as opposed to "Ich bin kalt" which would imply youre a cold person). Or perhaps "zurück" is too literal for this usage in german and may only be used to express "to go back", which I see on computer/GUI interfaces normally.
Ok I just looked it up on LEO and I believe you can use ,,zurück" in this manner, a la "zurück sein" which means "to be back." Mystery solved.
"Ich bin da wieder angekommen, wo ich gestartet bin." yes it is possible, but not for the sentence above from Duolingo. And it sounds still better with the 'wieder' before the 'da', because we point much more often to the time in this sentence. ~Again here! I am there where I started once.