How to Reduce TTFB?

hi, we have a site and hosting at, choosing VULTR High frequency with RAM 4GB, Processor 2 Core, plugin: wp-rocket, Autoptimize, couopns text is the name of a website we have, while the TTFB are higher than 200ms, we have tried many method, it still not work to improve TTFB.
Please Help me to speed up my site’ TTFB.