Need to reskin an existing application

I have a simple app and a source code. You need to completely reskin the app (update all 60 pages). Start from the beginning (1st screen). Then you have to take care of their responsiveness for android and ios devices as well. It's a whole lot of mess on some pages.
there is no complete flow of design in Figma file although small flow is there like modules wise but not overall complete app.
I need the 1st screen to be updated TODAY.