String reversal, capitalize vowels, lowercase consonants
We have a namespace called StringOperation,
a class called Program,
and methods called Main,
ProcessInput, Shift,
regions called Entry, Logic.

Looking from a high level,
this program could do anything,
as these terms are completely meaningless.
Strive to find more meaningful names for your program elements,
so that readers can have a clue what the program is about without having to fully read the implementation.
If I can see in front of me the logical pieces of the puzzle,
the mental burden of understanding what goes on in each element would be much reduced.

I know that all self-respecting programmers know by heart that 97 means the ASCII code of the letter A, 101 the letter E, 105 the letter I, ...
Wait a minute, no, actually that's not a requirement,
I don't think anybody should have to know at a glance what these numbers mean in your case statements.
A better way would be to write like this:

case 'A':
case 'E':
case 'I':
// ...