In some cases, your IP may be locked by the Synology NAS, for example, the email host is installed on the Synology NAS, and the email password is incorrectly set.
Or Synology did not correctly set the forward header of the real IP on the internal network. No matter what the reason is, we want to remove the locked IP through the command line.

The following is an example of my operation

ssh root@cc

Synology strongly advises you not to run commands as the root user, who has
the highest privileges on the system. Doing so may cause major damages
to the system. Please note that if you choose to proceed, all consequences are
at your own risk.

root@CCC:~# sqlite3 /etc/synoautoblock.db
SQLite version 3.34.1 2021-01-20 14:10:07
Enter ".help" for usage hints.
sqlite>

After entering

delete from AutoBlockIP where IP = "locked IP";< /pre>
You can also view it under the select command
select * FROM AutoBlockIP;
To leave, you can Next command
sqlite> .exit