Learn English – The attachment has “already been sent” or has “been already sent”

Both indicate an action that occurred (and was completed) in the past. The

In principle the perfect tense is used to indicate that an action or circumstance occurred earlier than the present time (or other time under consideration) and often focuses attention on the resulting state rather than on the occurrence itself. In your example

You can use the account that you’ve already created.

the emphasis is on the fact that you can now use the account because you have already created it in the past.

I've tried to help you... seems to wait for something more that is happening today.

I've tried to help you, but you are still making the same mistakes.

It is different than I tried to help you (...?) There is no expectation that it be tied to the present.

I tried to help you, but I could not.

The standard English expression for solving a problem that has already been solved is...

Reinventing the wheel
duplicate a basic method that has already previously been created or optimized by others

The idiomatic push at an open door has a completely different meaning...

to achieve what you want easily because a lot of people agree with you or help you (usually in continuous tenses)
The campaigners are pushing at an open door because most local residents support their campaign against the new road.