In my post that is for changing the forward slash to backward slash. Now i am asking fo changing the backward slash to forward slash.

Then you need to swap the part that is searched with the part that is replaced.

Currently, as haukex already explained, you have:

#           delimiters
#             |  |  |
#             v  v  v
$localdir =~ s/\//\\/g;
#              ^^ ^^
#              |   |
#    search part   replacement
[download]

So, if you swap search part and replacement, you get:

#           delimiters
#             |  |  |
#             v  v  v
$localdir =~ s/\\/\//g;
#              ^^ ^^
#              |   |
#    search part   replacement
[download]

The above gets much clearer if you use another delimiter instead of s///g, for example, s{}{}g. Then your original line is

#           delimiters
#             |  ||  |
#             v  vv  v
$localdir =~ s{/}{\\}g;
#              ^  ^^
#              |   |
#    search part   replacement
[download]

With the swap of search part and replacement part, that becomes:

<c>
#           delimiters
#             |  ||  |
#             v  vv  v
$localdir =~ s{\\}{/}g;
#              ^^  ^
#              |   |
#    search part   replacement
[download]