If you can't change the device IP, you may need to change your network setup from 10.x.x.x range to 192.x.x.x in the router perhaps.
Is all this in one physical location?
What device are we talking about, something you have that has a static IP and you really can't change it?
What did you connect to it when you tried to change it?
What's it connected to? Sounds like a totally private network (192...) as is yours (10.x.x.x)
Try to describe the physical connections of all these things.
Some clarification of your setup and what's required might lead to few answers on this forum. Until then, it's clear as mud.
I promise NO answers, just trying to have YOU describe things better so someone might understand what you're facing.