Hi Guys, I have a doubt. when the guest shopper places an order from the webstore he doesn't have login credentials then how could he manage with returns ? How SCA handles this situation?

I am pretty sure there's a lead record created for guest shoppers.. is the sales order not linked to a shopper?

Yes when the guest shopper places an order then in backend customer record is created as a guest shopper and the salesorder is linked with that. But how he can manage returns in the webstore? As he don't have logins to goto myaccount and place the returns

You wouldn't be able to manage returns in the webstore unless the lead record became a customer record with valid login credentials.