I have created a react native using app and created an apk for that using expo. Now I have to make some modification in that app. So do I need to build that again using build:android? or Is there any method to modify content in bundled app
If you have the over-the-air updates that expo offers enabled (I believe it's enabled by default), then whenever you publish your app (expo publish), the app on your phone will update automatically (you don't need to download the new apk). That also works when the app is on Play Store.
The way this works, is basically the app requests an updated js file from a public url on launch and runs that js instead of the old one. I personally dislike this approach so I disabled OTA updates for my app. In case you do too, then, you either need to manually listen for updates in your app (please refer to the above link) or install the new apk every time you build a new version (this is only useful in development).