Build on what you know and on what you are confident about. From what you describe, this is most likely:
- You were hired and trained as a developer.
- You didn't expect to be assigned to project that has no coding.
- You want to be in development.
- The reasons why you want to be in development are to keep gaining knowledge and experience.
Given above, consider approaching your manager about as follows:
A while ago you asked me why do I want to do coding. I gave it a thought and here are my reasons. I was hired and trained as a developer. I did not expect an assignment to project that has no coding. I want to be in development in order to keep gaining knowledge in Java and experience. Given that, would you please consider my transition to development project?
Depending on their response, conversation could go further and I am not going to predict how (neither should you), simply because it's impossible to read their mind to do so.
One general advice though, if it turns out that things look like going in the way you dislike - say, if manager insists on keeping you there, and doesn't provide compelling reasons for that - try to avoid getting into argument with them.
The reasons for this are, first, that it's generally a bad idea (as discussed eg at WP.SE) and second, the very fact that they don't want to utilize trained and willing developer, makes rather prominent red flag.
The one absolutely solid place to store your capital today — if you know how to do it – is in software developers’ wallets ...this is the one investment that will weather the storms. It doesn’t matter whether you are an individual or a corporation, or what corner of the world you inhabit. You need to find a way to invest in software developers... (The Rise of Developeronomics)
Manager aware of the above would rather ask self a question like, why I don't utilize such a valuable resource properly? is this negligence justified?
The way you describe things makes one feel they didn't bother, which in turn suggests their rather severe ignorance - and that it could make little sense to try convincing / educating them... but there's too much "if's" here to go into further details - just ask a new question if things turn out like that.