That particular tomato has what is called catfacing.
Not a disease.
Instead, the fruit was set while temps were relatively low.

Yellow leaves are often due to one or more of the following:
- too little fertilizer;
- too little water OR too much
- have gone dry one or more times.

So, please tell us what you have done and/or are doing.

And also post 2 pictures:

- one of the ENTIRE plant

- at least one image of an individual damaged leaf