How to reduce the time complexity of the function below

from itertools import permutations
def next_bigger(n):
    nlist = list(str(n))
    perm = permutations(nlist,len(str(n)))
    perm = set(perm)
    listofperm = ()
    nlist = int("".join(nlist))
    for x in perm:
        form = int("".join(x))
        if form < nlist:
            continue
        else:
            listofperm.append(form)
    listofperm = sorted(listofperm)

    if (listofperm.index(n) + 1) == len(listofperm):
        indexofn = listofperm.index(n)
    else:
        indexofn = listofperm.index(n) + 1 
    return listofperm(indexofn)

I’m trying to get the next bigger number by rearranging the digits of n but my code is very inefficient can you suggest ways to make my code more efficient and faster

inputs would be any integer