How to modify words in a line using perl oneliner

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,
I would like to modify the word "first" into "last" in the second line of file one.txt could you kindly help.

Input File(one.txt)

#verify_custom
fleet part=first base=first
after base
[download]

I tried the following perl one liner, but it did not help. perl -ni.bak -e 'print s/first/last/' one.txt

Expected Output:
#verify_custom
fleet part=last base=last
after base
[download]

Thanks a lot.