Blackmagic Design does not release standalone “patches” for beta versions. Instead, they release new beta builds (e.g., Beta 4, Beta 5) that replace the previous beta entirely. If you are looking for a patch to update from Beta 3 to a newer version, you must download the full installer for the later beta from the official Blackmagic support site.
If you meant you need help fixing a specific problem in Beta 3 without updating, let me know the exact issue (OS, hardware, error message) and I can provide a workaround. Blackmagic DaVinci Resolve Studio 16 Beta 3 Patch
Here’s a helpful piece of information regarding and the concept of a “patch” for it: they release new beta builds (e.g.