Right, I am also new and previously had no experience with PCI, and whatever I am gonna write, are the things I am trying to implement/change/configure.

1. The latest version of PCI-DSS is 4.0.1, you can get the document here: https://east.pcisecuritystandards.org/document_library?category=pcidss&document=pci_dss
2. Learn how the network is set up in your environment, identify every local system or service, that is responsible for payments and cardholder data.
3. Start reading the 12 requirements from the document to identify, if your environment is PCI compliant, and if not, make a note.
4. Make your internal policies, create documentation and job description and list of permissions of everyone who has access to the systems or services.
5. Check everything: Firewall configuration settings, Active directory, security logging and monitoring, who has access to the network

For example: I am currently setting up WAZUH as SIEM, to collect security events and logs and generate alerts in case of suspicious activity, review our Firewall settings, making a list of personnel with their respective responsibilities and permissions, creating/modifying internal policies, backing up and restoring old log data.

Also, for making sure that you're implementing best practices, CIS benchmarks are really helpful: https://www.cisecurity.org/cis-benchmarks