Openhab2 : Connect Modbus Energy Meter

I have got new single phase energy meter with modbus protocol and wifi enabled.
Now I am not able to create a thing on openhab for the same. Even though Device is connected to Wifi, i am not able to know the ip for the same. Any leads will be appreciated to configure energy meter as slave in openhab2

You can’t, unless you can find out the IP address.
Maybe your router can tell you what address it assigned.
You might also need to take steps to prevent it changing the IP address in the future.

Whenever I am trying to delete old modbus slave , poll and data from ui ,it says 409 Conflict and does not allow to delete. What can be the issue

Did you create them from PaperUI in the first place?