The friend remembers how to use A and B a bit incorrectly.
A : iyoiyo いよいよ
B : yoyaku ようやく, yatto やっと, toto とうとう, tui ni ついに
The meaning of A and B is very close, but not always same, some cases are same,
but A can not be used in this first sentence case,
the second sentence can be used with either A or B.
Correcting the first sentences to correct Japanese is,
= I finally found what I was looking for.
The second sentence is,
= Yeah!(or Yes!), the final (stage/episode or something) will be coming soon,
reached now, or finished(just now, not so long ago), the truth has appeared.
"iyoiyo" may feel like an onomatopoeia(オノマトペ, 擬声語 giseigo, 擬態語 gitaigo)
bc the same sound repeats twice, but this is not, one of "adverbs 副詞 fukushi".http://daijirin.dual-d.net/extra/giseigo_gitaigo.htmlhttps://en.wiktionary.org/wiki/Category:Japanese_adverbs
And this is not important, although this -ze ぜ and -nda んだ(= no da のだ) is
an ending 語尾(gobi) of "emphasis form(強調形 kyocho-kei)" used among friends
or similar relationship, but this "iyoiyo" also means emphasis as pleasure or expectation.
But, -ze ぜ is used by young men mainly, women use -wa わ usual,
also -nda んだ is used by young men mainly, women use -no yo のよ usual as standard Japanese.
This specific end form is one of "otoko kotoba 男言葉" and "onna kotoba 女言葉", https://en.wikipedia.org/wiki/Gender_differences_in_spoken_Japanese
however, although more complicated in dialects = hogen 方言,
you will eventually find similar qs in books(comics, novels) anime, dramas, movies, games and more.