頑張れば

if (someone) works hard, if (someone) does their best

→ 頑張る
頑張れ do one's best, persevere + Conditional (if/when)
verb · conditional Rare #39,589
if (someone) works hard, if (someone) does their best
JA: 頑張れば、きっと試験に合格できます。
EN: If you work hard, you can surely pass the exam.
Conjugation of 頑張る

もっと頑張ればよかったんだよ

I should have tried harder.

頑張ればいっぱい貰える

The harder you work, the more you'll get.

— 動くな、死ね、甦れ! (1990)

勉強さえ頑張れば

As long as you work hard at your studies

— いまを生きる (1989)