Disable route propagation in AWS Transit Gateway
Remove a propagated route from a route table attachment.
To disable route propagation using the console
-  Open the Amazon VPC console at https://console.aws.amazon.com/vpc/ . 
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            On the navigation pane, choose Transit Gateway Route Tables. 
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            Select the route table to delete the propagation from. 
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            On the lower part of the page, choose the Propagations tab. 
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            Select the attachment and then choose Delete propagation. 
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            When prompted for confirmation, choose Delete propagation. 
To disable route propagation using the AWS CLI
Use the disable-transit-gateway-route-table-propagation command.