VRoid Mobile doesn't have a video recording feature, but there is a method for you to shoot a video while using the app.
If you're using an iOS device, you can shoot videos by tapping the Record button from the Control Center if you add Screen Recording in Settings > Control Center > Customize Controls.
Refer to the following article for more details.
▼ How to record screen on iPhone, iPad, and iPod touch
https://support.apple.com/ja-jp/HT207935
If you're using an Android device, you can shoot a video of your screen by using a recording app.