Any tutorial on how to publish kotlin lib to maven central from gradle project. I have never pushed anything to maven central.

Mostly the same way as for Java. This guide also can be useful for you https://guides.gradle.org/building-kotlin-jvm-libraries/ There is guide for local repo publishing, but it’s similar for remote. You also should read guide how to register account on maven central, it’s not easy (much easier to do that on jcenter)