It's on the power steering bracket on the driver's side of the engine. Loosen the big bolt that the pulley spins around, then turn the long skinny vertical bolt in the bracket on the left side to move the pulley up or down to loosen/tighten the belt. After it's all back together, tighten it so the belt can barely be deflected no more than 1/2" max when pushed hard
by your thumb at the belt's widest unsupported distance. Then don't forget to retighten the big bolt the pulley spins around.