Restore WordPress Site Ownership Error

My site, www.newrattanagency.com, went offline right after I tried to move full WordPress ownership from my previous developer to myself and ran one last plugin/theme update. Since then the front-end shows only an error page—nothing loads... (Budget: ₹600 - ₹1500 INR, Jobs: CSS, HTML, PHP, Troubleshooting, Web Development, Website Management, Website Optimization, WordPress)