Mass update of valid from date field for many users

I want to update valid from date field in su01 transaction for 100s of users.

There are many users whose valid from date is not maintained, so I want to copy it from user create date and paste it to valid from date.

And create date is different for all users. Is there any transaction using which I can do this? Or ant SQL script or abap program through which I can achieve this?

Please tell me if any one have any idea..

Thanks.