Hey there
Do you keep the default boot password? If there, follow these steps
1: reboot the AC6605
2: press Ctrl+B enter the Bootrom , use password huawei (new version start V200R002 use password Admin@huawei.com)
3: after enter the Bootrom, follow this step:
input 7 then enter----------input yes then enter------input 1
4: when the system reboot, input the new password twice, then the systam will start up
5: after system start up finish, use the new password login the device
https://support.huawei.com/enterprise/en/knowledge/EKB1000080249
Hope this help