As Yin&Yang say the Aliens Bureau in Chania is in the main police station which is on the Chania to Souda road. Coming out of Chania it is on the left hand side between where it changes from a one way to a two way system and the traffic lights at the junction with Agnostou Gogoni.
Not everybody got their current EU Residence Certificates, either blue or beige, from there so it is not absolutely certain that we will need to go there and we won't know for sure until the government announces what the system is. On the one hand it is where third country nationals would normally go to get a biometric residence card so, since we will be third country nationals, it would be logical to go there. On the other hand, the files with all our details are currently held in local police stations around the area so it would also be logical to go to that police station. We will find out which it is in due course. There is no need to panic. The absolute earliest cut off is the end of June 2021 and it could be later than that.