Hello, friend!
1. Generally, you can press and hold the power button on the ONT for 10 seconds to reset the ONT.
2. You can log in to the web page to restore the settings. The detailed operations are as follows:
In the navigation tree on the left, choose System Tools > Restore Default Configuration. In the pane on the right, click Default to restore the factory defaults.

For more information about the HG8145V5, visit: HG8145V5
Thanks!