By comparing each letter in "ROAD" with the corresponding letter in "URDG":
'R' → 'U' (+3 conversion of R to U)
'O' → 'R' (move from +3 to Oh Ri)
'A' → 'D' (A to D is permutation of +3)
'D' → 'G' (+3 conversion of D to G)
Each letter in the alphabet moves +3.
Now we can use the same shift (+3) for the letters in "SWAN":
'S' → 'V'
'v' → 'z'
'ก' → 'D'
'n' → 'to'
So "SWAN" will be written as "VZDQ" in this code.