Search for "NPA 201-EV" on this forum and on Github. There is code on Github to change the address: https://github.com/AmphenolAdvancedSensors/Novasensor/blob/master/NPA700_ChangeAddress.ino. You have to check if that code will work for the 201-EV.
jremington is right about I2C address 0x00. That is the broadcast address, and devices with that I2C address are not supposed to reply with an acknowledge. That means the Arduino Wire library can not use it.
If they are indeed accidently at I2C address 0x00, and they do give an acknowledge, then you can alter the I2C Scanner to scan I2C address 0x00 as well.
The I2C Scanner will not change things, you can safely use it.