The upgrade reset the credentials to factory defaults. Solution: Use the hard reset button. Then try the default username/password combinations: admin/admin , admin/1234 , or look for a sticker on the router itself.
Only if you cannot buy a new router. Security vulnerabilities in outdated firmware are serious. If you cannot find a 2018 or later firmware, replace the router (e.g., a TP-Link Archer VR series). Firmware Upgrade Huawei Hg530