A hacker has found my IP address. So, I've started to use SoftEther VPN through the instruction of this video to hide my IP. I would like to ask if my late action to hide my computer IP still works?
Your IP address is something relatively easy to retrieve by different means. It's not a security problem if someone found yours. Your IP is just the address of your computer (or more likely your router).
Let's say that your computer is your house. The IP of your computer corresponds to the address of your house. You have to give the address of your house to access multiple services, there's nothing wrong with it. If you take care to lock your doors and close your windows, a burglar will have a hard time to get inside. It's the same with your computer, you have to keep it locked by frequently updating its software. In your house, you do not open your door to an unknown person, even more if this person wants to make you an offer too good to be true. It's the same with your computer: don't read e-mails you do not expect (especially their attachments, they could be trapped) and use an ad-blocker.
Using a VPN will just give you a false sense of security. That will not significantly improve your resistance to a hacker determined to harm you. That will not protect you against random threats (such as viruses or phishing attacks). Using a VPN is like telling people you're named John Doe: you will appear suspect and this will not stop a burglar to pay a visit to your house.