How to add babel plugins for my project?

[buglessir]

I'm using the umijs to implement a project. I've installed a package but that is using the nullish syntax in JavaScript and I've to add this package into my babel config:

{
  "plugins": ["@babel/plugin-proposal-nullish-coalescing-operator"]
}

but how can I add additional babel packages for umijs project?
I've read the documentations but it doesn't help me to config it...
Thanks