I Jest got a 7 year old zu and he won't eat dry food unless I mix it with wet food How can I get him to eat jest dry food

The first thing I would do is have his teeth checked by a vet to make sure that part of the problem isn't due to poor dental health which is may be causing him pain or discomfort.
At 7 years he is likely to have have some dental issues.
After that is done gradually add less and less of the moist food with each feeding until you have gone to just dry.