Sorry but i can't trust you. There are lot of recovery service, you are a newbie here...
I know with one hash of my wallet you can hack it and get all my money.
I just need to know how to use btc recover to recover just one letter of my password.
No worries, it's important to be careful. If you happen to be in Australia, I would be more than happy to meet in person. I'm in Melbourne.
Otherwise, I wish you the best of luck! Unfortunately, I do not believe you will not be able to recover just a single character of the password (without recovering the full password). That's possible in some situations where the clear-text password is stored in a database, but I'm not aware of any method to do that with this type of encrypted password. That would sort of defeat the purpose of strong encryption.
However, it is interesting that you say a single character might help you remember the password. That leads me to believe it is something based on a real word or sequence of words. If that is the case, you might be better off working to collect robust wordlists and transform rules than simply brute-forcing ever possible character combination. This may give you a better chance of success with limited time and compute resources.
You can search Google for password wordlists and rules, and use tools like hashcat for a different approach. I plan to write a full tutorial on this within the next two months, and I would be happy to share it when it's ready.
Good luck!