How to overflow across to nearby memory address

Question

https://code.sololearn.com/c15Qzq2a4p7p/?ref=app

I want to manipulate 0028ff23，to influence 0028ff22, is it possible for this compiler, or mix some assembly code?
at the start, I imagine that make a,b,c,d become char which is 1 byte. a and b are neighborhoods in memory.
then intentionally int *p , which is 2 bytes then make *p more than 1 byte . some complier can do this but it won't overflow to nearby memory address