Hello @Vaibhav Goel,
There are many resources for DCRUM migration in the community. https://community.dynatrace.com/community/display/LEARN/DC+RUM+Step-by-Step+Migration+Guide+to+12.3.... provides in-depth information on understanding the entire migration process to 12.3. Let me know if you have any questions on the migration process. Hope this helps you
Earlier this year, I also upgraded from 12.2 to 12.3 (although it was 12.3.0 at that point). Besides the issues in 12.3.0, your upgrade to 12.3.4 should be quite smooth and the new interface feels much nicer.