Hi, friend.
1. You can use either of the following methods to restore the ONT factory settings:
Touch and hold the RESET button for a long period of time (longer than 10s) to restart the ONT with factory settings.
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, as shown in the following figure.

NOTE: The preceding operations will restore factory defaults. Exercise caution when performing this operation.
2. HG series products (HG8245)
The default user name and password of a common user are as follows:
V300R016C10 and earlier versions: root/admin.
V300R017C00 and later versions: root/adminHW
For more information about the ONT login account and password, visit the following link:
Huawei ONT login account and password
Thanks.