SELECT @@SERVERNAME

select ag.name, ag.is_distributed, ar.replica_server_name, ar.availability_mode_desc, ars.connected_state_desc, ars.role_desc,
ars.operational_state_desc, ars.synchronization_health_desc from sys.availability_groups ag
join sys.availability_replicas ar on ag.group_id=ar.group_id
left join sys.dm_hadr_availability_replica_states ars
on ars.replica_id=ar.replica_id
where ag.is_distributed=1
GO

SELECT ag.name
, drs.database_id
, db_name(drs.database_id) as database_name
, drs.group_id
, drs.replica_id
, drs.synchronization_state_desc
, drs.last_hardened_lsn
FROM sys.dm_hadr_database_replica_states drs
INNER JOIN sys.availability_groups ag on drs.group_id = ag.group_id;
[sql]

How to manual failover to secondary availability group
1. Run the above on primary replica of both availability groups (DB01 & DB03)
2. Record the "last_hardened_lsn" of AG1, AG2 anf DAG
3. Change the primary availability group (DB01) to secondary role
[sql]
-- Run this on DB01
:CONNECT DB01
ALTER AVAILABILITY GROUP [DAG] SET (ROLE = SECONDARY);
[sql]
4. Run this on DB01 and DB03
[sql]
SELECT ag.name
, drs.database_id
, db_name(drs.database_id) as database_name
, drs.group_id
, drs.replica_id
, drs.synchronization_state_desc
, drs.last_hardened_lsn
FROM sys.dm_hadr_database_replica_states drs
INNER JOIN sys.availability_groups ag on drs.group_id = ag.group_id;

-- Run this on DB03
:CONNECT DB03
ALTER AVAILABILITY GROUP [DAG] FORCE_FAILOVER_ALLOW_DATA_LOSS;

-- Run this on DB01
:CONNECT DB01
ALTER AVAILABILITY GROUP [DAG] FORCE_FAILOVER_ALLOW_DATA_LOSS;