How to allow other people test my react native app on their iPhone and Android devices?

I'm a web developer and just new to the mobile world, I wonder how I can allow another people to test my app on their device remotely? For example, on the web app, I will create a staging environment (stg.example.com) and then they can easily test it from everywhere. But I can't found the same way for mobile app (react native). I can install the app to my phone through a capable, but I can't do it on my customer phone :sad:

Do I must publish it to App Store/CH Play first and then they can install and test it? It seems a bad idea :sad:

I really appreciate any advice, Thanks!