Revert back to an IP after changing to static from dynamic

We have a VM that I thought was using a static IP but it was set to use.
 The IP changed this morning and now it can't communicate with some external services. I have updated the network config to use static. But, can I change the IP to use the old one that is configured in the external vendor's firewall?  It changed today to newIP.
 It connects to a couple other servers and the old IP is whitelisted which is why it would be a huge help to switch back to that IP.