Hi @simigireesh, welcome to the community!
What you ask is not simple. That’s the power that comes with a really robust framework like Frappe and powerful application like ERPNext.
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Take the tutorial. This will help you understand what you’re getting into and a lot of context as to why ERPNext is constructed the way that it is.
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Get under the hood with some of the concepts has established in the JS Microtemplating pattern. My “aha” moment didn’t come until I read the frappe.render_template source, so I’d recommend that you do that.
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While I haven’t personally looked into it further than a search, I think you’re looking to apply the above techniques to these html templates.
Good luck!
-T