13 weeks out from lower face/neck lift. Have cording and hard lumps under chin - how do I fix this or will it go away? (photo)

There appears to be significant swelling within the skin. Some of those is expected after a facelift. Thermal damage created by a laser or ultrasound can create a problem that will take considerably longer to resolve. Do You know whether or not the skin was treated with a laser or ultrasound?

Although time should be helpful I would recommend starting steroid injections at 3 months to try to alleviate some of the problem. You will probably require revision surgery at the 6 month mark and that helps. Some of this advice is based on generalities because we do not the exact type procedure performed.

Thanks for the pictures.  I would agree with your plastic surgeon.  Time is the best treatment to allow the area to soften.