Well as Saraa has cleared that its not a automated feature and that after 3 months the WL will be reduced automatically. The member has to request for the reduction of WL and it will be reviewed by the moderator and it takes time.
BTW if the moderator feels that the member is still not adhering to the forum participation guidelines they may choose not to decrease the WL so its not a mandatory thing that the affected member will request and it will be done immediately and during the review process if the member gets another WL that further clears that the member is not ready for a WL reduction.
Regards,
121