Convert enum type back to enum

I am using a library which has an enum like the following

enum TestEnum {
  FIRST = 0,
  SECOND = 100,
  THIRD = 200,
  FOURTH = 300,
}

It’s not exported, but used in another class type like the following

declare class TestClass {
  testEnumProp: TestEnum | string | null;
}

Now I need that enum for my own code, but I can’t directly use it since it’s not directly exported. So I tried something like the following to extract the type

type TestEnumType = Exclude<NonNullable<TestClass['testEnumProp']>,string>

Which worked in the following case

const val:TestEnumType = TestEnum.FIRST;

But since I do not have access to TestEnum directly, I can’t use TestEnum.FIRST and have to use my extracted type

const val2:TestEnumType = TestEnumType.FIRST;

But it doesn’t work since TestEnumType is a type, but not the enum itself. This is the error I receive on my IDE.

'TestEnumType' only refers to a type, but is being used as a value here.ts(2693)

Any idea if I can somehow use TestEnumType.FIRST using some TS magic?