Hey there
In order to become an IES officer you need to clear an entrance exam called UPSC ESE exam. It has three steps prelims, mains, and interview. You need to clear all the stages and then you'll be selected. Check the link for detailed information regarding ESE preparation
https://www.google.com/url?sa=t&source=web&rct=j&url=https://competition.careers360.com/articles/ese-preparation-tips/amp&ved=2ahUKEwiM6NbCyq7pAhW04nMBHSxsCVsQFjANegQIBxAB&usg=AOvVaw1em4fwkcpKDmmU2KZ496-O&cf=1
Good luck
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