Navigate to https://app.tallbob.com/contacts/opt-outs

Drag and drop your CSV file into the grey box 
or Click "Drop file here or click to upload"

Please find the screenshot below for a sample file format that you could upload

Select the Data column that matches the phone numbers you want to upload to your Opt Out list

Then click upload

You should see a confirmation message in the platform that your Opt-Outs are being processed.

Uploaded SMS OptOuts successfully scheduled for import

Uploading a list of Opt Outs