There is not really a kotlin to java converter yet, but one thing you can do is compile your kotlin code to jvm byte-code and then run a java decompiler. The code you get needs some cleaning up to be usable, but I guess it is a start.
But I don’t think there is any good reason for JetBrains to build a kotlin to java converter. If a company would start using a kotlin to java converter they would be using kotlin anyways. In that case it is easier to switch the entire build system to kotlin instead of having both versions working parallel.
The java 2 kotlin converter is not used to write code in java, then convert it to kotlin and then compile. It is used to make the switch from java to kotlin easier. So why would JetBrains build a tool to switch form kotlin to java?