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).