How to find ordination date to Elder?

My father was ordained an Elder by his older brother who later left the church (though it appears his records still exist). My dad doesn't know what date his brother was ordained to the office of an Elder.

How would my dad go about finding this information?

Thanks!

If your father is still an elder, then his brother is in his priesthood line of authority. In that case, he can request his entire line of authority by following the instructions at Priesthood Line of Authority.