You need to access the Star Car Wash offer through the Linkt or LinktGO app.
Linkt Customer Rewards is available to all Linkt and LinktGO account holders (excluding passes and Commercial Accounts). So, if you have more than one person on your account, there's no need to share the offer. They simply need to log in to the Linkt or LinktGO app with their username and password to access the rewards.