First you need to know if the "external IP" of the Windows Server network is fixed or not, being fixed just know the address, then the next steps are:
Set the "local IP" of your Windows Server (maybe this step is already done, so I understood your site, since IIS is already released)
Free mysql port that should probably be 3306
(default) on VirtualServer
with the machine's local IP, as I described in external access with wamp (ignore the no-ip part if your IP is fixed)
It is worth noting that this example I followed in a basic equipment, being a complex network it is best to request the release of the 3306
port to the network administrator (s)
If your network is simple after you've released VirtualServer > Forward, then just try to access from another network, such as a network 3g or 4g by CMD
the command:
telnet x.x.x.x 3306
Change x.x.x.x
to the external IP that is used on the Windows Server network.
Extra: If your IP is not fixed and your network is simple / home for you to access IIS and mysql externally you will need to configure no-ip as described in the link in "step 2" (above), then after releasing via no-ip just test the port in cmd (using a 3g or 4g network), a dummy example:
telnet meusite.no-ip.biz 3306
Extra: I do not have many details of the network, the examples above are for a "simple network", perhaps the network is more complex recommend that releases the door for you, he'll know how to do it easily.
Then if this is the case, after the administrator confirms that you have released the port and you have a valid HOST (or fixed ip of such a network), just use one of these two or 4g):
If it's just the IP:
telnet x.x.x.x 3306
If you have a "configured hostname":
telnet meusite.com 3306