Second Surgery to Remove Extra Skin Left from Blepharoplasty?

It is very common to have persistent swelling of the upper eyelid skin after surgery at 3 weeks, especially if fat was also removed. It may also be due to sagging brows causing more skin present before the surgery.
Therefore, I would wait at least 3-6 months to allow complete healing before any touch up removal of more skin. Then you can really determine if the eyelids are not symmetric.
And I would revaluate the position of the brows and if they are contributing to the extra skin fullness, you may consider an endoscopic brow lift. It is important not to remove too much skin of the upper eyelid, resulting in difficulty closing the eyelid or lagophthalmos.

Revision Surgery

Revision eyelid surgery should be done at least 6 months
after the initial surgery to allow time for healing and tissues to soften. Asymmetries, excess skin, fat rolls, fat malposition can all be improved. Other treatments may include laser or
chemical peels to tighten skin and improve texture

Assuming you didn't originally need a brow lift, I'd give this surgery some time before making a decision on its success. Three weeks isn't much time. You still likely have some swelling which will detract from your final result. Give it a couple months before approaching your surgeon about a touchup.

Since it has only been three weeks status post blepharoplasty, it is important to wait at least three months prior to undergoing revision eyelid surgery. This can be done easily under local anesthetic after full healing has taken effect, when all the swelling has subsided and the incisions have healed.

On occasion, there may be a small amount of extra skin on one or both upper eyelids following Blepharoplasty. In these cases, it is very easy to conservatively excise the excess skin with local anesthesia. However, three weeks post-op is too soon. The perceived excess skin may be related to post-surgical swelling. I would be inclined to wait at least three to six months before considering removing any apparent excess skin from the upper eyelids.

A LOT of "EXTRA" upper lid skin excess is the result of sagging brows. If this goes unrecognized or is ignored by your surgeon, the result of an upper Blepharoplasty will always be extra skin.
WHY? Sagging brows contribute to excess upper lid skin. As this amount of skin increases, we increasingly use our forehead muscles (Frontalis) to keep the brows lifted as high as possible. This always results in the transverse creasing you see in older people. If instead of shortening the forehead / lifting the brows, an inexperienced surgeon chooses to remove the little skin "excess" of the upper lid, all the muscles will do is work less and drop the brows a bit resulting in "extra" skin. In effect, going after this skin is chasing one's tail.
See a Plastic surgeon (www.Plasticsurgery.org) and see if you need a Brow lift BEFORE having another potentially misdirected procedure.
Dr. P. Aldea

It is unusual for an experienced surgeon's patients to need more skin taken out after an upper bleph. Are you sure yours is a Board Certified Plastic Surgeon or Facial Plastic Surgeon? Either way, you need to wait 3-4 months to be sure you really need more done and to let the swelling go away. Also, you need to have the brows evaluated as the other doctors have said.

Eyelids are very fragile, and it takes time to heal after eyelid surgery. Until you heal completely, you can't really tell if there is extra skin left. A little swelling can make the eyelids look very different, and as you know, eyelids swell very easily. Six weeks after eyelid surgery, you will probably have a better sense of whether or not you need additional surgery. But I would wait 3 - 6 months before scheduling anything, just to be sure it is necessary.