I have the hash, the salt and the number of iterations and need to get the original password.
Is there an online tool to get the password from the pbkdf2-sha256 hash given the salt and number of iterations?
I have found online some tools that generate the hash given the password, salt and number of iterations but not the other way round.
Not within a reasonable time. The idea behind cryptographic hash functions is, that they are easy in one direction (Clear text to hash) but incredibly hard the other way around.
What you do to verify a password is you hash the entered clear password and then compare the hashes. You don't "unencrypt" the stored password hash and compare the clear text.
You can read more about cryptographic hashes application in password verification Wikipedia
There are some methods to attack hashed passwords. Most notably the brute-force attack, where you try out passwords, then hash them and compare against the given hash. You can improve on that attack using a dictonary attack, where you narrow down the search space by using a dictonary because many people use words instead of random characters.