@Aam_jmp,
A couple of things, you will need to index into the list of names , not use the list as a whole.
for(i = 3, i <= N Items(a1), i++,
dt << Rename Table Script(a1[i],Names[i]);
);
Another thing, I would keep in mind is if you are starting from i = 3, Are you sure you want to be naming starting from the 3rd column of dt1 - if yes, the above should work.
Best
Uday