How to set and access multiple credentials for only one asset value?

Based on your requirement, you can create in a folder a Credential asset.
The asset will not be set as a Global Value and you will provide multiple credentials for different users.

Note: You cannot provide multiple credentials for the same user in the same asset name.

Example:

Make sure that your users are having Assets View permission in the folder where the Asset was created.

More details about Assets can be found here: