How do I convert input string to hash and back to original string in console window at the same time in C#

You can't.
Hashing is not encryption: encryption can be reversed, provided you know the algorithm and key used for encryption. Hashing cannot: it is the process of producing a number from a string of text. The hash is normally considerably smaller than the original text and is generated in such a way that it is unlikely that some other text will produce the same hash value. But because most of the original data it "thrown away", it is not possible to reverse the process and get back to the original string.
If you have four numbers: 10, 14, 18, 49 you can "encrypt" them by adding the index multiplied by e a "key value" to each number. If we have a key of 2, the the encrypted data would be 10, 16, 22, 55 and you can decrypt that back to the original by reversing the process. (It'd be a rubbish encryption algorithm, but...)
The hash version might work by adding each value together to produce 91. But you can;'t get back to the original from just 91: it could be 1, 1, 1, 88, or 1, 1, 2, 87, or ....