первым: the first or firstly / the first time?

Юрию Гагарину сообщили, что он полетит первым за несколько дней до старта. Некоторые считали, что если предупредить космонавта заранее, то он будет волноваться, потеряет слот, аппетит.
My trouble is with первым, according with the place where it is put "он полетит первым" one has the right to translate "he should fly the first", but the mention to предупредить космонавта заранее indicates that it refers to сообщили. "They announced to Y. G. the first time that he sould fly some days before the taking-off". However I don't see первым as an adverb I see in the dictionary phrases like первым делом, with the meaning of an adverb.
So I think that this word is in the phrase quoted misplaced, isn't it? Thanks.

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according with the place where it is put "он полетит первым" one has the right to translate "he should fly the first"

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That's right.

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but the mention to предупредить космонавта заранее indicates that it refers to сообщили.

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It doesn't exactly refer to первым.
The second sentence explains why he was told that he the one who will fly only a few days before the start (not in a more long period of time).

Thank you and a Happy New Year.