By Default Oracle ASM don’t allow remote sysdba connection since ASM instance is in NOMOUNT state. You Might get ORA-12528: TNS:listener: all appropriate instances are blocking new connections error when you are trying to connect ASM instance remotely. To bypass this error you need to add UR=A in the tns files like example below and connect as sysdba:

ASM =

  (DESCRIPTION =

    (ADDRESS = (PROTOCOL = TCP)(HOST = xxxxx)(PORT = 1521))

    (CONNECT_DATA =

    (SERVER = DEDICATED)

    (SERVICE_NAME = +ASM)

    (UR =A)

  )

)