If I understood correctly, SDET(Software Development Engineer in Test) implies you also have some programming education and can probably make a much faster transition into development than a beginner. If anything, I feel your background will only help you become a stronger candidate in the future.
To get into backend, I recommend taking a certificate course online(Coursera, Udemy, edX, etc) on NodeJS or .net or a similar popular backend technology. You might have to climb up the ladder again but I think smaller companies and startups in your area would definitely be willing to try you out over a complete fresher in the field. Make a capstone project using what you learn on the course, show it to people, show it to potential employers, and generally do what you can to get a competitive edge. Best of luck!
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