If your product has been around for more than a year, your icons probably tell that story. Some came from a free library, some were custom-made, a few are screenshots of things that almost matched.
The result is an icon set that looks like it was assembled by multiple people across multiple years — because it was.
Fixing this used to mean hiring a designer to audit and redraw everything. That's expensive, slow, and easy to defer. So it doesn't happen.
A different approach: pick the icons you actually like. The ones that feel right for your brand. Use those as your style reference.
Upload a screenshot, circle the icons that represent the look you want to keep, and generate new versions of everything inconsistent. You're not replacing your design language — you're extending it. Everything new will match what's already working.
The difference isn't dramatic in any single icon. But across a full UI, visual consistency changes how professional a product feels. Users notice it without knowing why.