Change Oracle SYS user Password

 . /opt/oracle/db/tech_st/19.3.0/prodcdb_erpdb.env

cd /opt/oracle/db/tech_st/19.3.0/dbs

cp orapwprodcdb orapwprodcdb.orig

mv orapwPROD orapwPROD.orig (File doesnot exists)

orapwd file=/opt/oracle/db/tech_st/19.3.0/dbs/orapwPROD password=manager123* entries=10 ignorecase=y

orapwd file=/opt/MG/oracle/PROD/db/tech_st/12.1.0/dbs/orapwPROD password=mikmanager entries=10 ignorecase=y

orapwd file=/opt/MG/oracle/PROD/db/tech_st/12.1.0/dbs/orapwTEST password=mikmanager entries=10 ignorecase=y

Now execute:

Connect Sqlplus / as sysdba

alter user sys identified by <password>

Bounce DB

If SYS user can connect with wrong password as well.

Edit sqlnet.ora file and add:

SQLNET.AUTHENTICATION_SERVICES=(NONE)