If you want to restart just the JS part, then you can use React Native Restart Package. This will work on both Android and iOS.
If you want to restart the whole application, There are no react native packages as of now. If you want to create on your own, then check the following link
Building the custom Android module for React Native
If you find difficulty in writing the base JAVA code, You can generate the boilerplate using React Native Create Library
UPDATE:
From 0.62, React Native have added DevSettings.reload(). So, if you want to reload programmatically while developing you can use that. Note that this method does not work in production!
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