You need a full size keyboard.
That can be attached to the back of the operator/monitor/keyboard pendant.
There are two unused plugs all the way to the left. Move the existing plug to the top left. Plug the full size keyboard beneath it. Those two plugs are nothing more than a jumper.
The root problem is the CMOS back up battery on the mother board. There are a ton of posts about this. Search for them.
In a nutshell, because of the age of the machine, the possibility of the original mother board being inside the machine is slim. But if your mother board has a NiCad CMOS battery, it will leak its guts out and ruin the mother board. The NiCad type are soldered onto the mother board. Others may have a coin style lithium battery. Still others may have a "real time clock chip/IC".
Change the battery and then enter the CMOS. Because there are dozens of varieties of CMOS it would be difficult to tell you what to input.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)