Welcome, new fren
Here's a list of in-game commands that will prove to be helpful: https://www.phantasystaronline.net/forum/index.php?/tool-box/commands/
Oh. I've walked someone through the process before but I've never actually done it myself. XD
Honestly, I've got no clue what's causing that 'Old password is incorrect' dialog.
• First you enter your information at Account recovery. • Following that, you'll get an email with a key. You copy/paste that key at Password change — into the 'Old password / Key' field and proceed to enter a new password.
Enter the username or email associated with the account here: https://www.phantasystaronline.net/forum/index.php?/account-management/account-recovery/
Follow the instructions in the email to reset the password.