How to crack the password of a wallet?

[Myleschetty]

I only have the keystore file. I have lost the password of them. I don't have any seeds.

You don't the wallet seed before you can recover the Ethereum wallet and through the Keystore file because the Keystore file also contains the wallet's private keys. If you know the first 5 alphabets or the number of your wallet privacy key you'll easily spot the wallet privacy key. I don't know how the MyEtherWallet operates now but it allows restore the wallet through the use of a Keystore file.
Check it if it still functions that way.

[Jawhead999]

You don't the wallet seed before you can recover the Ethereum wallet and through the Keystore file because the Keystore file also contains the wallet's private keys. If you know the first 5 alphabets or the number of your wallet privacy key you'll easily spot the wallet privacy key. I don't know how the MyEtherWallet operates now but it allows restore the wallet through the use of a Keystore file.
Check it if it still functions that way.

In order to access his wallet via Keystore file, he need to type his password too, that's make him can't access his wallet.

I think if @OP didn't remember few characters of his wallet, we can assume he already lose his wallet because brute force will take a lot time and it's not efficient. This is why everyone and developer always advice people to save the seed phrase, you don't have to worry if you know the seed phrase.

[gurunanakji777]

If you have access to any of the following: Keystore File, Passphrase, or Private key, you can retrieve your Ethereum wallet from any system. However, if you lose all three items, I doubt you'll be able to access your wallet.

[raidarksword]

Resetting password from your wallet is easy as long as you have the private keys that will unlock your wallet once your import it from other wallet apps but if you don't hide and stored the keys safe then it's difficult to do so. That's why keeping the keys are important in times if you need them in the future like this.