I find it easier to do the other way around: renam...

# gradle

[Czar]

I find it easier to do the other way around:
rename build.gradle to e.g. old-build.gradle
create build.gradle.kts with following content:

import org.gradle.kotlin.dsl.*

plugins {
	`java`
	kotlin("jvm") version "1.2.31"
}

apply {
	from("old-build.gradle")
}

Then move parts of code from groovy to build.gradle.kts.
This way you have your fully working groovy setup called on to from kotlin-dsl entry point.