You need to ask your doctor what the cause of this is. This normally is just a slight drop but not back to its original position. If you have it and had an Endotine it may have come loose and needs to be repositioned. See you very experience surgeon if you have to have further surgery.
There are two common causes of what you are referring to . First, your eyebrow ptosis (drop) can be caused by injury to the frontal branch of the facial nerve during the procedure. If you are unable to physical elevate your eyebrow this is most likely the issue. Nerve function will return in many instances. Botox administration of the opposite brow, effecting lower the opposite brow, can help to camouflage the issue while the nerve heals. A second cause might be failure of the fixation device that was used to suspend the brow. I would suggest following up with your operating surgeon for careful evaluation and diagnosis. Good Luck
What type of forehead lift did you have? For most brow lifts, dissection is done over the temple area. This can either damage or stretch the nerve in this area which is responsible for elevating the brow. If you lift up your forehead, does it move on the right? If is doesn't you have some nerve issues on that side. It usually resolves but can take a few months. You will start to see some motion in the forehead, and the brow will start to come back up. If this is not the case, you will have to have the right side lifted again.