You use your favorite reversing tools. IDA, Ghidra, x64dbg, binary ninja, etc.

For this particular example, Photoshop, an error message is displayed for currency detection. The first thing I would do is load up the executable and look for that particular string. If I'm lucky and there aren't many protections for the executable, I'll be in the right area for figuring out what to patch, or I'll at least know which code paths to start tracing.

The single instruction patch mentioned in the parent comment is probably changing a conditional jump (for example JE - jump if equal) into an unconditional jump, or a NOP (no operarion) instruction that does nothing, depending on if the jump leads into code we want to run or not.

JMP 0x"target"

Everyone else has mentioned the easy part - replacing the function entry with "return not money"

The hard part is finding where that is. One approach is to start with the error string - find it in the file and put a memory-read breakpoint on it in the debugger. Trigger the error and capture the call stack - start working up the chain until you identify why that text was read, either the failure directly or a message passed to that thread - if it's a message, find what sent it and why.

Given the detection code is in a separated library, it should be relatively easy (supposing the code is not obfuscated) to find out where it is loaded/called.