Hello, friend!
To configure 5 GHz Wi-Fi for the HG8245Q2, perform the following steps:
First, use the administrator account and password to log in to the ONT web page.
Click the WLAN tab, and choose 5G Advanced Network Settings from the navigation tree on the left. In the right pane, configure the advanced parameters of the 5G Wi-Fi network.

2. Click Apply.
Thanks!