どうやって => how N5
てやってもらえるか => Could you please... help me? N4
Suggestion
以来 => since; henceforth ~ N2
てやる => Do for someone N4
Give and take advice
やっと => Eventually... N4
に行く/に来る/に帰る => go/arrive/go back (to do something) N5
てやってもらえないか => Could you...help me, please? N3
Suggestion
てやる => to do for; to do a favor (casual spoken) N4
Benefit
て[以来「いらい」] => After A, B (continuous action/condition N2
Information, Report
てやってくれないか => to do a favor; request a favor; do something for ... N4
Correction
やる => Give B to A N4
Give and take advice
... やっと => at last; finally (Realizing what is expected) N3
Completed