IP Address hunting on a raspberry pi can be a bit of a pain…
What are you using as your host machine?
- Linux
- Mac
- Windows
The reason is that in the Linux & Mac world there is a lovely little tool called avahi or bonjour on the mac that allows you to ignore IP addresses altogether and use the nice friendly name
zynthian.local
Unfortunately this can be set up on a windows machine but it involves quite a dance.which is documented somewhere on here . . .
That will give you a name and is VERY MUCH the preferred way of working…
It’s worth knowing that nowadays if a piece of kit can have a web interface and it will.
Your Internet router will probably have a helpful web page that you get to by typing the peculiar ip address 192.168.0.1 or 192.168.1.1 or something else 
into the web browser on a machine that is also attached to the same router.
You will probably need a username and password . . .Often they ain’t changed. That is a bad thing not to do . . . .
Don’t bother about why the number is like that it just is cos … history.
If you can get to the router and have connected your Zynthian Pi to the same router with an Ethernet cable. Yes they do need to be near each other for this …There is wifi but personally I don’t use it. If anyone can boot a zynth without running jack cleanly straight into wifi then things have changed since I last tried it 
But the web admin of your router may display the ip address of the raspberry pi it sees and that is one way of getting the ip address cos it’s your router that generally gives the addresses out, and they CAN change 
This is why using names is much more sane.
So put either the ip address or zynthian.local into the url section of your browser on your host machine. and you should see the webconf of the xzynth. This is where you set up the hardware that is connected to your zynhian.