Xcode - manually upgrading to Swift 4

I have a project with two goals, both goals contain over 99% of the code and were written in Swift 3.

When Xcode 9 is available, one of the targets is scanned, the codes and the Build Settings targets are updated for Swift 4. Unfortunately, I just learned that another target is still marked as Swift 3.2 syntax.

I would like to update the second target to Swift 4 using XCode, however the second target is marked as Swift 3.2 syntax, but the codes are already Swift 4, they don't compile and thus the automatic Swift 4 update with XCode did not work.

Since both targets have most codes, I don't need Xcode to help me auto scan or convert codes, I would like to update the whole project to Swift 4. I updated the "Swift Language Version" in the build settings of the second target for Swift 4.0 manually. Are there any other project settings I should take care of too?

thank