What is best treatment for tightening facial skin post filler use?

Skin tightening on the face is best addressed non-surgically by either ablative lasers for loose skin around the eyes or mouth, or RF microneedling (around the mouth). Lateral skin (jowls) can also be helped with muscle stimulation (TriLift/EmFace). Always be sure that the medical director of your spa is abl board certified plastic surgeon or dermatologist to ensure those overseeing your procedure avoid untoward complications.

Thanks for your question. Two of the most effective devices I have worked with for this indication are:
Sofwave- utilizing microfocused ultrasound to deliver heat to the deep dermis at a depth of 1.5mm, generating new collagen and elastin in the skin. It's a very popular treatment also as it has no downtime!
Morpheus8- utilizing RF energy delivered at the tips of micropins. With this approach you get the collagen stimulation of the heat PLUS the collagen stimulation of the microneedling, so you can potentially get more result per session, but at the expense of 'some downtime'- puffiness, faint redness for a day or two, potential bruising. Morpheus8 could of course also be combined with PRP.
Both work very well, both require topical numbing.
Both have smaller handpieces designed for use in delicate regions such as the under eye- the Sofwave one is called the "Precise" handpiece, the Morpheus has the "Prime" Tip.
Both are very safe though in particular with the Morpheus8 I would be careful to go to a provider you can firmly 'trust'- based on reputation, reviews, and/or recommendations of others, as this one can cause a burn if technique is not good on the part of the provider. I hope that helps!