If your router is bootlooping or unresponsive, flashing standard firmware via the web GUI is impossible. You must use hardware or bootloader-level recovery methods. Method A: CFE HTTP Recovery Web Server
The BCM63381B0 is supported by OpenWrt (though sometimes as "target: brcm63xx"). A full OpenWrt image gives you: bcm63381b0 firmware full
This contains the applications, web interface (GUI), and configuration files. If your router is bootlooping or unresponsive, flashing
Because Broadcom does not provide public downloads, enthusiasts typically use the following methods: Vendor Repositories: web interface (GUI)