If you want to reset CPanel user account password using SSH then run below command.

whmapi1 passwd user=username password=passwordtoreset

Above command will change the password of the user. Kindly replace the username with actual username and password with the actual password with which you want to reset it.

It wil show output like below

[root@ ~]# whmapi1 passwd user=abcdedfg password=12sdfsdfsdf
--- 
data: 
  app: 
    - system
    - ftp
    - mail
    - MySQL
    - postgresql
metadata: 
  command: passwd
  output: 
    raw: "Password for “abcdedfg” has been changed.FTP (File Transfer Protocol) password change has been queued.\n"
  reason: Password changed for user “abcdedfg”.
  result: 1
  version: 1
[root@ ~]#