Unfortunately AWS does not advertise and prefer specific IPs to ASNs directly by request. Typically with BGP when making such changes, you'd advertise a /24 and not a single /32 to have the preferred route out through TATA. These types of changes would affect multiple customers.
I understand that you cannot distribute your application globally, but perhaps you can put additional services in place to support your external customers. I would take a look at Global Accelerator as it may be a good fit to help optimize traffic paths for your customers.
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