As others have mentioned there's no quick way to convert react to react-native.
A possible alternative if you want your react app to run on a mobile device without rewriting your codebase is to use Cordova. For fun I ported a react-web app into a mobile app using Cordova in just a few minutes. There are some drawbacks to this method, but the benefit is that you can have a working mobile app in very little time.
Below are the steps if anyone is interested in a Cordova workaround alternative:
REACT SETUP (done in command line)
>1. npx create-react-app my-app
>2. cd my-app
>3. npm start
DEPLOY TO STATIC:
>1. Update your package.json file from your my-app directory to add "homepage":"." (see below)
"name": "my-app",
"version": "0.1.0",
"private": true,
"homepage":".",
"dependencies": {
>2. Build (in command line) npm run build
CORDOVA INTEGRATION (in command line)
>1. cd ../ (change to wherever you want the project created, don't do this inside your existing react app folder)
>2. npm install -g cordova (only if you already don't have Cordova installed)
>3. cordova create MyApp
>4. cd MyApp
>5. cordova platform add ios //or android or browser
ADD A COUPLE STEPS FOR INCLUDING YOUR REACT PROJECT
>1. Open your Cordova MyApp www folder, delete all files and folders in it except for the 'js' folder
>2. Back in your react build folder update the index file to add two cordova scripts:
<script type="text/javascript" src="cordova.js"></script>
<script type="text/javascript" src="js/index.js"></script>
>3. copy all your files from the react build folder into the Cordova www folder (replacing everything except the js folder)
BUILD REACT-CORDOVA APP (in command line, inside your Cordova project)
>1. cordova build ios //or android or browser
TEST OR DEPLOY TO STORE ETC.
>1. Use xcode to open open your react-cordova .xcodeproject, this can be found in the MyApp/Platforms/ios/
>2. Select your simulator and run. Enjoy your new mobile app!
TWEAK
There are some minor tweaks you'll need to do (like remove the tap delay...etc)
-I think this is why people think Cordova apps are slow, but it's an easy fix...