Downloading a single DLL file from third-party "DLL fixer" sites is generally discouraged by experts. These files can be disguised malware.
Since opencl.dll is part of your GPU software, the best fix is to install the latest drivers for your specific hardware.
Often, the error is caused by a corrupted driver installation, meaning other related files might also be missing. How to Properly Fix OpenCL.dll Errors
If the version you download doesn't match your specific graphics driver, programs may still crash or fail to open.
Instead of searching for a manual download, use these safer methods to restore the file: