Need marketing strategy as SHOW HN didn't work.

You should completely change your expectations considering the effort of marketing. Marketing is a constant effort which many people say is about 50% of your total work.

So there is no "making a quick post anywhere and people will come and love your product".
Most startups fail because they suck hard at marketing and not at programming or product idea. I really recommend you to dig deep into this topic. Here is a reading recommendation:
https://www.amazon.de/Traction-Startup-Achieve-Explosive-Customer/dp/0241242533

Wow. You really over valued SHOW HN. Your question is to wide, try to learn a little bit more and ask specific questions, will be easier to help.