You can reset the root password in iDRAC Settings page in BIOS during boot or reset using local racadm commands. You can refer below link with more details [URL] 
I have a R640 unit that had a custom idrac password tag but has since been lost. Is there a procedure for resetting that custom password if the tag is no longer around? I've tried restore all idrac defaults via F2 and trying to hard code a new password but no luck.
Reset iDrac Random Password without info tag R640