https://m.wikihow.com/Tighten-Loose-Neck-Skin
I found the above article. I would only consider the exercise and moisturizer section for myself, none of the injections and botox and surgery etc. My neck is not bad for my age but I do have 'jowls' at the sides of my jaw that I hate.
I saw an old episode lately of Alfred Hitchcock and the wife in the story had one of those straps under the chin and tied on top of the head, to firm a double chin. Do those things work? It would probably give ME a headache, like when I use a too tight headband.