"Getting the first value of a field then populating it to another field"

[Blitz]

Hello anyone knows how to implement this scenario.

When filling the "assign to" field of an incident form, the first value of the "assign to" must be copied & auto populates the "First Assignee" field, the first assignee field only captures the first value of the assign to, it must not be overwritten & the first assignee field is read only.

[Zach Koch]

Here is a mock onChange client script, couple of things to note:

You'll need to the change the name of first_assignee field in the script to your field name
This also assumes that your first assignee field is a reference to sys_user, if it isn't then you'll need to get the user's name field value to put in that field.