when it comes to; concerning; in doing
A formal expression used to introduce a matter, occasion, or action under consideration: 'when doing X,' 'with regard to X,' or 'in connection with X.' Often appears in instructions, announcements, and written explanations.
When signing the contract, please check the contents carefully.
When it comes to introducing the new system, it is necessary to listen to opinions from the workplace.
Before using the service, please read the following terms.
について is a neutral, general 'about/concerning' that works for any topic, while にあたっては is more formal and specifically ties the statement to an action or occasion.
Grammaticalized from に plus the te-form of 当たる and topic は. The verb 当たる has senses such as 'to correspond to' or 'to apply to,' which supports the expression's meaning of addressing a particular occasion or matter.