Step 1.) make sure they are on the correct website https://campus.hesperiausd.org/campus/portal/hesperia.jsp
Step 2.) Make sure they are using their correct Username
Step 3.) Have them try the default 6 digit date of birth and first initial of first and last (i.e. John Smith 01/01/1901 would be 010101js)
Step 4.) From the Student/Parent Portal click the following. Help -> Forgot your password?
as long as they put in a recovery email address (if it's a student hopefully their student email address) they will get an email with a link they can use to reset their password themselves.
Step 5.) If you get to this point put in a ticket on HelpDesk and your site CLS/TSS can assist further.