How am I expected to pull in a Maven dependency not available on Maven Central?

I’m embarking on a journey of an open-source contributor. I am fairly familiar with Spring Cloud Gateway so I decided to contribute to that framework. However, I’m a first-timer so I encounter some set-up issues that I didn’t encounter before as a developer of my own projects

I forked and cloned the fork of the repository, didn’t yet introduce any changes, but Maven build failed. It’s because the project has a dependency on org.springframework.cloud:spring-cloud-dependencies-parent:pom:4.1.1-SNAPSHOT which is not available on Maven Central (it is available here)

I don’t think I’m supposed to tinker with the pom files and define custom repositories

So what reasonable assumptions can I make in this situation? Should I manually add that jar to the project? If so, can you describe the process in more detail (I use IntelliJ)?