You could using PowerShell to loop through all Documents in the specific subsite Documents Library, and then check in them.
Please open Windows PowerShell as an SharePoint admin and run the following script.
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script to check in the documents only from subsite , those documents showing already checked out option for many documents. Please help in sharing the script only for subsite
You could using PowerShell to loop through all Documents in the specific subsite Documents Library, and then check in them.
Please open Windows PowerShell as an SharePoint admin and run the following script.