On-Page SEO For Two Sites

I have two live websites that need a focused on-page SEO overhaul with the single goal of driving more organic traffic. All existing content and design will stay in place; what I need is a thorough optimisation of every on-page element that influences search visibility... (Budget: ₹600 - ₹1500 INR, Jobs: Content Management System (CMS), Internet Marketing, Keyword Research, Link Building, Marketing, SEO, Shopify, Website Audit, Website Optimization)