The Set Temp Password link appears for users under Core > Users > Edit User Profile Data > search/select user > Sign In Information:

User-added image

If the Set Temp Password link does not appear, this is likely because the user is LDAP enabled.

To check your LDAP enabled roles, navigate to:
  1. Core > Security > LDAP Authentication.
  2. If "Enable LDAP" is marked, then you have users that are LDAP Authenticated.
  3. Scroll through the roles to see which are enabled:

User-added image

If the user's role is LDAP enabled, the user's password must be reset on the LDAP server by your IT department.

Read more about LDAP 

This could also be caused by the Account being Temporarily Disabled/Locked.

To see if a Users Account is Disabled/Locked, navigate to:
  1. Core > Users > Edit User Profile Data
  2. Search/select the user that does not display a Set Temp Password Link
  3. Scroll down to Sign In Information, and see if the Disabled/Locked checkbox is marked
  4. If it is marked, click Edit, mark the Disabled/Locked check box
  5. Click Save & Exit