Currently there is no plugin through which i can upload the android and iOS build in saucelabs.
Step 1 : .apk/.ipa file is generated on bitrise.
Step 2 : Upload the newly generated android and iOS build in saucelabs.
Hello @s.sankalp 
This step is supposed to upload an apk to SauceLabs and executes Espresso Tests: https://www.bitrise.io/integrations/steps/saucelabs-espresso-app-automate
Does this help? 
To upload your Android and iOS app to Sauce Labs from Bitrise, first ensure that Sauce Labs is integrated with your Bitrise project. You can do this by adding the Sauce Labs step to your Bitrise workflow, where you will need to configure it with your Sauce Labs username and access key. Then, set up your Bitrise workflow to build the necessary app files: for iOS, you’ll need to generate an .ipa file, and for Android, an .apk or .aab file. Once the build completes, the Sauce Labs step in the Bitrise workflow will automatically upload the generated app files to Sauce Labs for testing.
After uploading your app, you can run tests on various devices and configurations provided by Sauce Labs. For example, if you are testing an iOS game like Brawl Stars Nulls iOS, ensure that the app is correctly uploaded and tested on various iPhone models and iOS versions. This integration allows you to automate testing across multiple platforms, so every time you push a new build, it is automatically uploaded to Sauce Labs and tested, streamlining the process of ensuring your app works seamlessly across different devices.