You don't mention how old you are and this will be relative to whether or not the the skin tones up again. Well it isn't the skin but the muscles that need to be worked.
It will be hard work and take months, possibly even years, but if you are committed, give it a go.
Despite me loosing weight several years ago, I have never been able to really tone up my legs and thighs, and I've been a gym bunny, runner, pilates goer for the past 30+ years! Sadly for me I think it is genetics, so I just grin and bear what I have now!
But still look good for my age!