How to find the original value from the keccak 256 hash value in python?

I'm using following code to get the keccak 256 hash:

import sha3
k = sha3.keccak_256()
k.update(b'age')
print (k.hexdigest())

How do I convert the keccak 256 hash value back to original string? (I'm ok with using any library as needed).

You can't convert the hash value back to the original string. The hash function is created in a way that it is infeasible to convert the hash value back to the original string.