Why don't you try to make up for the time you wasted?
Literal
Wasted time [object-を] take-back [conditional-たら] how [copula-なの].
~たらどう(なの) = 'how about doing X?' — a suggestion pattern. 取り戻す ('to get back, to reclaim') is a compound (取る + 戻す). The final なの is feminine-softened explanatory. A gentle nudge disguised as a question.