Open up winrar,(pick a file or make 1 called test)click add file. A menu opens, click tab advanced on top and a new menu opens and on right side is set password button and also when winrar is open up on top the click file a drop down appears, there is a option set default password. I havn't used the password option in a long time, just to password protect my 1 file.
Seems to me I set password when I made the zip file. Hope this helps.