1- check Primary and standby database role and status.

select name, open_mode, db_unique_name, database_role from v$database;

2- Check primary and standby for any gaps.

On primary:
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select STATUS, GAP_STATUS from V$ARCHIVE_DEST_STATUS where DEST_ID = 2;

On standby:
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select NAME, VALUE, DATUM_TIME from V$DATAGUARD_STATS;

3- Check primary database status.

On primary:
===========
select SWITCHOVER_STATUS from V$DATABASE;

You must see TO STANDBY or SESSIONS ACTIVE.

4- convert primary to standby and later standby to primary.

alter database commit to switchover to physical standby with session shutdown;
startup mount;
select name, open_mode, db_unique_name, database_role from v$database;

5- Convert standby to primary.

Our primary is already converted to standby. Now it’s time to convert original standby into primary

select SWITCHOVER_STATUS from V$DATABASE;
alter database commit to switchover to primary with session shutdown;
alter database open;
select name, open_mode, db_unique_name, database_role from v$database;

6- On new standby – Initially your primary database: Start MRP

alter database recover managed standby database disconnect;