thank you everyone for your prompt response.
i am managing at least 17APs via DHCP ,all of them are AP305. 16APs were successfully discovered with no console or hard reset done except for 1AP. actually I was able to modify its APName and group until I noticed it goes up and down every few minutes.
never had a chance to neither plug console nor do hard reset since it was already mounted up on ceiling
will test your suggestions next visit.
thank you all