How to freely switch between VR mode and normal mode during runtime(using HTC vive)

My apologies for take up your time. I’ve encountered a tricky problem and I’ve been triped for a long time. On 4.25.4 version, I would like to be able to freely switch between VR and normal mode during engine runtime. I’ve tried many methods from this forums, but none have worked. I hope someone can provide me with some ideas. Thank you.