John Gill Commentary Exodus 29:19

"And thou shalt take the other ram; and Aaron and his sons shall lay their hands upon the head of the ram." — Exodus 29:19 (ASV)

And you shall take the other ram
The other of the two that was left, (Exodus 29:1) :

and Aaron and his sons shall put their hands on the head of the ram ,
as they were to do, and did, upon the head of the other; (See Gill on Exodus 29:15).