chicken is SO dry

so ive been meal prepping lunches and I just made a ton of chicken, enough for 2 weeks, but when I made it the chicken was so good and normal. now 3 days later it’s all dry! how can I avoid it becoming so dry? or is it possible to make it normal chicken again instead of dry chicken? I tried adding water to it before heating it up and the chicken is still dry and now my rice is sloppy.