Hey Sandeep
We encourage developers to unlock their blog on Hashnode, add a custom domain and use it as their primary blog. It has a lot of advantages over creating your own. However, if you already own a blog elsewhere, you can still utilise Hashnode's audience by republishing the same post here. We regularly tweet good articles and place the best ones in our weekly newsletter. You also gain exposure because every article is pushed to Hashnode feeds.
We support setting custom canonical URL which indicates the original content to search engines -- this is to make sure your original blog is not penalised by Google for content duplication. While republishing on Hashnode, you can simply enter the original article URL and we take care of the rest.
Similarly, if you use Hashnode as your primary blog we encourage you to republish those articles on other platforms that support custom canonical URLs. That way you grow your reader base without worrying about content duplication.

Further reading:
What's Canonical URL: hashnode.com/post/hey-developers-own-your-canonic…
Republishing - Why & How: townhall.hashnode.com/why-you-should-republish-yo…