Corrupted workbook recovery

The first thing I'd recommend is making a copy of the workbook and leaving the original untouched. If it's stored on a network drive, USB stick, or a cloud-synced folder (such as OneDrive), copy it to your local drive before trying any recovery steps.

Then in Excel, go to File > Open > Browse, select the workbook, click the arrow next to Open, and choose Open and Repair. Try Repair first. If that doesn't work, repeat the process and choose Extract Data, which may recover your formulas and values even if the workbook can't be fully repaired.

If the file is stored in OneDrive or SharePoint, check its Version History. Restoring a version from before the corruption occurred is often the quickest and most reliable solution.

If those options don't help, don't keep opening and saving the damaged file. Instead, check for:

An AutoRecover version.

A backup or previous version (for example, File History or your organization's backup system).

If you can share (without sensitive data):

the exact error message,

your Excel version,

the file type (.xlsx, .xlsm, etc.),

where the file is stored (local drive, network, OneDrive, USB, etc.),

and OS system,

I can try to suggest the most appropriate recovery approach.

Good luck—I hope you're able to recover it.

Before trying anything else, make a copy of the workbook and keep the original unchanged. If it is on a network share, USB drive, or cloud-synced folder, copy it to a local folder first and work on the copy.

In Excel, go to File > Open > Browse, select the workbook, then use the arrow beside Open and choose Open and Repair. Try Repair first. If that cannot open the file, repeat the process and choose Extract Data to recover values and formulas where possible. Save anything recovered under a new file name rather than overwriting the damaged workbook. 

If the file is stored in OneDrive or SharePoint, check Version history before spending too long on repairs. Right-click the file, choose Version history, and restore or download a version from before the problem started. That is often the cleanest recovery option. 

If neither option works, avoid repeatedly opening and saving the original file. Check for a backup copy, an AutoRecover file, or a previous version in File History. The Excel version, file type (.xlsx, .xlsm, etc.), storage location, and exact error message would help narrow down what can still be recovered.
Here are two Microsoft guides that may help:
https://support.microsoft.com/en-us/excel/repair-a-corrupted-workbook
https://support.microsoft.com/en-us/excel/restore-a-previous-version-of-an-excel-file