Hi @KarishmaCh1
In short, customer attributes supports multiple alias - assuming that the visitor may have different ids in your companyes backend. Allowing for creating an alias for a CRM id, email id, call center id etc.
You use the alias to specify what the alias refer to and will function as the key when you upload data to customer attributes.
The implementation of setting the alias and the relevant id is done in Adobe Tags (aka. Adobe Launch).
Since you're posting this in Target community I assume that you wish to use customer attributes together with Target, so there's actually a 'shortcut' you can take, as Targets parameter mbox3rdPartyId (https://experienceleague.adobe.com/en/docs/target/using/audiences/visitor-profiles/3rd-party-id) also can be used as a source/alias into customer attributes: https://experienceleague.adobe.com/en/docs/target/using/audiences/visitor-profiles/working-with-cust....
So if it is easier for you/your developers to set a Target parameter with the relevant id, then this is an option too.
