The code comes by email, but I can't activate the code to access my account in the game on the website as the email description says to change the game password; it is not appearing.

Hi, this is what you do:

1) Visit details page
2) Click: send email with a new unlock code
3) Get email
4) Paste code from email into LFS "GAME password"
5) Click unlock

The "GAME password" field you will find in LFS unlock screen. This is accessible by a button at the bottom right of the LFS entry screen.

i dont get email

Please check your email address is set correctly in your details page and check your spam folder.

i dont have my unlock code

Did you follow the steps that Scawen wrote above?

Hello, I couldn't access my old email address for the unlock code, but I learned that the code was received through the new email address.
However, even though I created a new email address, I still receive the error "This email address is in use." Any help would be greatly appreciated. Thank you.

It means that the email address is already used by another user account. Are you sure you don't have another LFS account with your new email address already?

To identify the account that uses your new email address, you can enter it on this page: https://www.lfs.net/loginreset and you will receive an email addressed to that user name.

It is the page for if you forgot your password. There's no harm in trying that.