"Is there a instrucction for this?"
Only if you want to force yourself into writing slow, complex, inefficient, obfuscated, buggy code:
"I need to change a string variable(x="Eval_E01") to a normal variable for example y=Eval_E01."
I doubt that you "need" to do that. In almost every case where a beginner writes that they "need" to use dynamic variable names, once they actually describe their usecase we can show them much better ways to achieve their task.
Rather than asking us about your anti-pattern approach, you should explain what your actual problem is:
