Neck fat and platysma - what would be the best treatment? (Photo)

Hi I'm a woman, nearly 58, had a total thyroidectomy in 2014. My surgeon said he stiched the platysma muscle after removal. The scar is not revisible but as I've aged, the neck skin is saggy and I've developed small flat skin tags. I have Xeomin injections in my frown and some in my DAO muscle, which has helped the jowling. The injector has suggested I have injectables in my platysma, as its too tight. Would this be the best treatment? I'd like something the lasts? Thank you for any advise.