Open IM and select Options > Blocking options > View blocked list.

To find a specific blocked instant messaging user, enter the first letters of the user's name. Matching names appear in a list.

To allow messages to be received from a blocked IM user, scroll to the user and select Options > Unblock.

To prevent messages from being received from other IM users, select Options > Block new contacts. Select the IM user from your IM contacts or enter the user ID.