Are the FTD and the FMC on the same subnet? do you still see the FTD from the FMC? did you try to ssh into the FTD from within management subnet or through a L3 device? when you console into the FTD, issue the command show network and check that all the settings are still there, if so, try to issue the command ping system <your FMC IP or default gateway>.
You welcome Vishal. Changing the management IP address of the FTD would not require removing the FTD from FMC and re-add it. What you could do is changing the management IP address on the FTD, and then going on the FMC and changing the FTD management IP in Devices > Device Management > click on the device > Device > Management > click the pencil icon and change the IP in there.