ExpectedOut.java

import com.something.Inner;

public class Test {
    public static void main(String[] args) {
        var one = new Inner();
        var second = new Inner();
    }
}

Rewrite.java

import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import org.openrewrite.InMemoryExecutionContext;
import org.openrewrite.Result;
import org.openrewrite.java.ChangeType;
import org.openrewrite.java.JavaParser;
import org.openrewrite.java.tree.J;

public class Rewrite {
  public static void main(final String... args) throws Exception {
    final InMemoryExecutionContext ctx = new InMemoryExecutionContext();
    final List<Path> paths = List.of(
        Paths.get("/path/to/Test.java"));

    final JavaParser javaParser =
        JavaParser.fromJavaVersion()
            .logCompilationWarningsAndErrors(false)
            .build();
    final List<J.CompilationUnit> compilationUnits = javaParser.parse(paths, null, ctx);
    var recipe = new ChangeType("com.something.Outer.Inner", "com.something.Inner");
    final List<Result> results = recipe.run(compilationUnits);
    results.forEach(result -> System.out.println(result.diff()));
  }
}

Test.java

import com.something.Outer.Inner;
import com.something.Outer;

public class Test {
    public static void main(String[] args) {
        var one = new Inner();
        var second = new Outer.Inner();
    }
}