How can I know or change the address of slave (pressure sensor in my case) in RS485 communication?
Read the datasheet?
Hi and welcome to this forum,
RS-485 only covers the hardware part of a... type of communication, not how rs-485-masters/slaves talk to each other or how they can be addressed. Anyone can develop a... way of addressing both as they please.
Sorry for saying so, but you more or less... ask for a tire, without mentioning what size it is, or which model of car you drive... 
Do you have a link to the sensor you want to use ?