ISA/IEC 62443 is the most important reference for Industrial Cybersecurity and it is the global standard worldwide. However, It is not the only one and you can find other guidelines or whitepapers that can help you. These are NIST 800-82r2; NIST Cybersecurity Framework; NIST Cybersecurity Framework Manufacturing Profile; BSI ICS Security Compendium; among others.

If you do not know what IEC 62443 is, you can find the following webinar where you can be introduce to it and learn some concepts about how to protect your OT environments.

Enjoy it!