Install the entirety of the iSeries access for Windows software CD. (Client Access) onto your PC.
There’s an application called Operations Navigator.
It’s a very windows looking system management tool.
There is a user management function that will allow you to add/change/delete users and groups.
Just like with Active Directory you can right click a user ID and change the password very quickly.

This tool is great if you have multiple AS400 systems or LPARs because you can perform these management functions from one location. No hopping from one green screen to the next.

This tool is included with the purchase of the AS400 and can be viewed as free.

There’s many management tools out on the market but that’s going to require $$$.
I personally dig where BSafe is going. Their package rolls in admin tools with security compliance and reporting.
Powertech Group is also very good. (I use them currently) and there’s HELP Systems.