Great question Aji. Asked by many!   Learn. Network. Read. Gain experience. Learn. Attend events. Experiment(safely!). and learn....   

Tripwire have a good intro page. There are many many others... https://www.tripwire.com/state-of-security/7-top-technical-resource-providers-ics-security-professionals

Try the OPSec 210 courses - free - you will know the OT stuff so that helps a lot.  https://www.cisa.gov/ics-training-available-through-cisa

Operational Security (OPSEC) for Control Systems (100W) - 1 hour
Differences in Deployments of ICS (210W-1) – 1.5 hours
Influence of Common IT Components on ICS (210W-2) – 1.5 hours
Common ICS Components (210W-3) – 1.5 hours
Cybersecurity within IT & ICS Domains (210W-4) – 1.5 hours
Cybersecurity Risk (210W-5) – 1.5 hours
Current Trends (Threat) (210W-6) – 1.5 hours
Current Trends (Vulnerabilities) (210W-7) – 1.5 hours
Determining the Impacts of a Cybersecurity Incident (210W-8) – 1.5 hours
Attack Methodologies in IT & ICS (210W-9) – 1.5 hours
Mapping IT Defense-in-Depth Security Solutions to ICS - Part 1 (210W-10) – 1.5 hours
Mapping IT Defense-in-Depth Security Solutions to ICS - Part 2 (210W-11) – 1.5 hours
Industrial Control Systems Cybersecurity Landscape for Managers (FRE2115) - 1 hour

Then there are the ISA and the SANS courses which are amongst the most recognised but not low cost.

There are many other training providers for lower cost - good search will finds them and look through LinkedIn. 

Good luck. There are lots of mentors around to help.  We NEED more OT Cyber people.

Thanks for the reply. Out of the CISA courses, i have done 2-3 of them like 100W, 301V,401V etc. and will do further progress. ISA and SANS are very costly courses which may cost more than 8000 dollars and it is very difficult. perhaps i will do one foundation module of ISA. was looking for some cheaper options. Thanks once again for prompt reply.

Do a course in ISA or IEC62443  usually done as a fundermentals course then you can do the other in any order which are for design, maintenance and risk asessment

Hi Aji,

The best ones I have done that would be applicable to you are the Exida IEC 62443 courses. For IACS (Industrial Automated Control Systems)

I have done the self paced online course CS100-IEC 62443; Automation Cybersecurity Analysis, Design and Operation.

A useful and interesting course with good content.

It is split into two courses:-

CS101:IEC 62443; Automation Cybersecurity Analysis

CS102:IEC 62443; Automation Cybersecurity: Applying IEC62443

At the end, if you take one online exam to gain CSP (Cyber Security Practitioner) qualification.

If you wish to take further training with them, you could do specialised courses for CACE (Certified Automation Cybersecurity Expert) or CACS (Certified Automation Cybersecurity Specialist)

Hope it helps.

There are other free courses online that can also be useful, but I think the Exida and maybe TUV are more recognised. 

Thanks for this info,