Do I require LWA to use this account linking starting from alexa app? please provide a dummy app link. and how do I get redirect uri from backend
LWA isn't necessary - you can use your own authorization server. If you are using app to app account linking, you would most likely be using your own authorization server, so you wouldn't use LWA in this case at all.
The redirect URI and authorization URIs are all supplied by you assuming you have your own authorization server, so if you don't have these then this is something you'll need to look into yourself. It might be worth going through the following documentation to understand regular account linking first, follow by app-to-app account linking documentation if you have your own mobile app that customers can use to log into your service:
Account Linking 2 Answers
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