That would largely depend on the make and model of the sat nav. Unfortunately I am not psychic (despite any assertions to the contrary on the part of my children) so I can't even begin to guess.
One would suggest there may be a connector marked "AV In" or "Video In"
It may be expedient to read the manual.
If you don't have a manual, reputable manufacturers usually make their documentation available online.
Acp
August 2017
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix satellite navigation.