(be for starting make sure you are using backtrack 5 or kali linux as operation system)
open the command line

fcrackzip -b -l 1-99 -u (your file address)

example

fcrackzip -b -l 1-99 -u /root/Descktop/thisisazipfile.zip

because we are using brutal force the -l is specifying the length of letters/numbers. In this example we are using 1 to 99 for the length because we don’t have any info about the zip but if you can guess the length of the password and change it to some thing less (ex: 5-10) it will be faster to find the pass.