I found solution here – https://forum.proxmox.com/threads/lost-access-to-the-gui-after-ssl-certificates-deletion.58789/post-271194
– remove the files '/etc/pve/local/pveproxy-ssl.pem' and '/etc/pve/local/pveproxy-ssl.key'
– run `pvecm updatecerts --force`
– systemctl restart pveproxy