I was thinking of transferring a client's website to a different server.

1. No one is managing it and I don't know the login information.
2. The WordPress version is too old and the server's Easy WordPress Migration feature cannot be used.

Two major problems with high hurdles were discovered.

1. Force creation of a WordPress administrator account

There are many cases where people do not know the administrator account, but we were able to successfully log in by forcibly adding administrator information via FTP!
→ How to forcefully add administrator login user information via FTP in WordPress

2. The problem of using an outdated version of WordPress

Although I was able to log in, I tried to use xserver's easy WordPress migration function, but the migration failed.
When I checked, I found that the version of WordPress was 5.1.19.
Currently it's 6.8.3, so it's pretty old.

If the WordPress version is too old, even if you use the popular All in one WP Migration plugin, the data migration will fail because the WordPress versions of the source and destination are too different.

Pay attention to the PHP version

If you do not configure PHP to match the version of WordPress from which you are migrating the data, the restoration will fail with an error.
→PHP Compatibility and WordPress Versions

Migrate your data with the WPvivid Backup & Migration plugin

I made an explanatory video!

The WPvivid Backup & Migration plugin is a plugin that allows you to issue a key from the destination site and then enter the key into the source site to migrate data.

Destination, Source
First, install and activate the WPvivid Backup & Migration plugin on both WordPress sites.

Destination site

• WPvivid Backup
• Backup & Restore
• key

Generate the key.

Source site

• WPvivid Backup
• Backup & restore
• Auto-Migration

Enter the key and click the Clone then Transfer button to automatically transfer.

 Automatic migration failure

 A server certification error occurred and automatic migration was not possible.
I also manually migrated the data, so I will show you the steps.

Create a backup on the source site

• WPvivid Backup
• Backup & Restore

This screen allows you to create a backup file.

Download it to your computer.

 Restore on the destination site

Upload the backup file you downloaded from the source site using the Upload button at the bottom of the same screen.

Just press the restore button and wait.

Finally, update your WordPress version.

Although there is a high possibility of an error occurring, we will update your latest WordPress version and revert your PHP version to the recommended version.
This time, the upgrade was successful without any errors! I was lucky.