Navigate to click "Login", then select "Non-海角论坛 Log-in for Contractors/Vendors". If you have never set up a password for your permit/account, you will need to select "Forgot password?" then enter the email address associated with your permit.
After receiving the email about resetting your password, repeat Step 1, then instead of submitting your email address again, choose the "I have a password reset key" link.
After submitting your new password, you will have to return to the login page, and again choose the "Non 海角论坛 Log-in" option, then enter your email address and the new password that you just created.
Click on "Permits" in the white section of the page (above the gold section). If you are doing this on a phone, the menu with the "Permits" option will be hidden until you click/tap on the three stacked horizontal lines in the upper left corner to open that menu (see second screenshot below).
Phone screenshot:
Click on "View" beside your current permit.
Click the appropriate button to "Add a new vehicle", or to make a "Temporary Replacement", or a "Permanent Replacement", or to "Remove Vehicle From Permit".
