you can work thu this like so

1. !! is shorter than a 5-character chunk, so it must be padded with u chars
2. decode !!uuu
3. bytes: [33, 33, 117, 117, 117]
4. subtract 33 from each byte: [0, 0, 84, 84, 84]
5. create 32-bit integer: (0 * 85**4) + (0 * 85**3) + (84 * 85**2) + (84 * 85**1) + (84 * 85**0) = 614124
6. break the 32-bit integer up into 4 bytes (this is an exercise for you). you will get: [0, 9, 94, 236]
7. because 3 u were added to the padding, drop 3 bytes from your result: [0, 9, 94, 236] becomes [0]
8. encode [0] as ascii string: '\0' or '\x00' or '\u0000' – each are equivalent

answer: <~!!~> decodes to a string with a single null byte: '\0'