First add your member to the online/mobile fraud block list.  Fraud Block lists are accessed via Tool #892 Update Fraud Block Lists/Blocked Persons List.  Select the Online/Mobile fraud block list and add your member to the list.  (You may wish to note that reason for this block using the Comments field.) 

Important note: This blocks the member's SSN/TIN from having online banking access.

Since your member has already logged in to their account, next block further access to the account. Uncheck Online Banking (and give a reason code), on the Update Audio/Online Access screen.  This screen is accessed via the PIN shortcut or Tool #14 Member Personal Banker, then Online Banking/ARU (activate, change PIN/Password; view access history).