Go to your storage account, navigate to "Firewalls and Virtual Networks". Select "allow acces from selected networks". Create a Virtual network.
You only have to enter a name and leave the rest default.
Save your settings to your storage account.
You'll see that "endpoint status" is disabled.
Visit your website again, you should get an error now since the website is not yet connected to the virtual network.
So let's connect the website. Go to the Networking part of the website and configure vnet integration.
Connect to the Vnet.
We need to enable the storage endpoint on the VNet.
Go back to the storageaccount in the portal, go to Firewall and virtual networks.
Click it and, open the "Default" subnet where it says "Endpoint disabled".
Go to the "service endpoints section" Tick the box on the Microsoft.Storage and press save.
Now it might take a while for azure to configure all your settings and networking.
You can try restarting your website and check if it works again in isolated mode by visiting it.