There are so many solutions to resolve this problem ethically but i am telling some basic which is maybe you already knew.
First of all if your first paper already publish and you are writing an other paper that paper showing 100 % similarity with first then you have to follow
1. make it your title of your research unique and different
2. With proper and different citation from first one
3. if you are using some material from first paper then also give proper citation with your own name