GSX develop, I want to Create a whole unit Mail-In repair(repair or replace),but it need some tier part ,how can I get the tier parts?

Note :User can add tier part a ccording to the coverageOptions mentioned in the request. For "No damage" scenario where user sets coverageOptions as empty, user should add the tier part in the request. For all other coverageOptions, in case user does not add the tier part, system will add the tier part as per coverageOptions entered. In case system finds more than one tier part for chosen coverageOptions, then the user will be asked to add the tier part of his choice.