I have a problem with my NAS TS-459 Pro+ running Firmware version 4.2.6. I can’t use myQNAPcloud Link because if I don’t install it, I can’t use myQNAPcloud. I can only access it locally from a remote server
Can you help me?
Open a ticket with QNAP and check if your very old system is even getting a version QNAPcloudlink that has access. If not, just get a router that support a VPN server. No need to rely on QNAP stuff to remote access.
do you have a guide for vpn
Not sure what kind of guide you need, do you have a good VPN router ? … If not buy one.
I advocate for ASUS routers (with modified Merlin OS) for consumer VPN
https://www.asus.com/ca-en/support/faq/1008713/
https://www.asuswrt-merlin.net/
RaspberryPi and OpenVPN would suffice:
before everything was working fine after I did the firmware update it stopped working remotely is there a way to reset everything and restore the factory firmware?
Have you opened that ticket ?
no, because from the nas it doesn’t allow me to open the ticket
Open it via the service portal
ok 
if you care to look at the top of the page and click on “Support” you can raise a ticket that way.
If you are using a RPi then Wireguard is a better option than Openvpn. There is also Tailscale on the NAS itself.