@Pragnya: you may want to review Web API Call for Report Print in HTML where @rmehta explains how to capture requests and JSON output for a custom report and then wrap such a request into your third-party app.
Another alternative is to customize your ERPNext instace where Android App is assumed to read Stock Ledger report data from. You may build a new custom function (inside a new custom app you develop) to return JSON with data from Stock Ledger report and then expose it for RPC calls (whitelist, in Frappe/ERPNext lingua franca) from external apps as explained in https://frappe.github.io/frappe/user/en/guides/integration/rest_api, RPC section.