If he would have tried, he would have succeeded.

"is tried" - Present tense is incorrect for past conditional$

$"was tried" - Simple past doesn't fit this conditional structure$

$"had tried" - Correct for past unreal conditionals (third conditional)

Here are the conditional structures with their basic forms:

Zero Conditional: If + present simple, present simple

"If you heat ice, it melts"

First Conditional: If + present simple, will + verb

"If you study hard, you will pass"

Second Conditional: If + past simple, would + verb

"If I had money, I would travel"

Third Conditional: If + past perfect, would have + past participle

"If I had studied, I would have passed"