Well, we don't host videos, so you'd need to upload it to a video hosting service (like YouTube, though if it's relatively short you can upload it to your social media posts) and post the links here.
As for getting a video in the first place, you'll need to be aware that GT Sport's replay files are not video. They're data, which GT Sport uses to reconstruct a race. To save video you'll need to play it back on your game on the PS4 (or PS5) and use the console's own Share features to capture it as video: