Step : 1 Go to FB BM > Setting > WhatsApp Business
NOTE : Select Correct WABA ID
Step 2 : Go to Business Settings. Click on WhatsApp Accounts on the left panel.
Step 3 : Select the relevant WhatsApp Account. Click on Settings
Step 4 : Click on OVERVIEW on the left panel.
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Step : 5
Choose the phone number or company name
Step : 6 Choose Two-Step Verification > Click Turn Off Two-step Verification
Step : 7
An Email will be sent to your FB BM admin Email. 
Open the Email title: WhatsApp Two-Step Verification Reset. 
Step : 8 You will be redirected to a confirmation page.
Step : 9 Confirm to turn off the two-step verification, and finish.