External drive pathes accidently mixed in a catalog file

I store my catalog file on an external hard drive. Windows assigns usually letter F to the drive. One day something changed and windows assigned letter H to the same drive. I did not expect it for some days. Yestarday I tried to open the catalog file but I need upgrade it first. After the upgrade the catalog file broked Lightroom. I have an old backup with 20 000 pics with this I could open Lightroom. With the very last backup containing 30 000 pics Lightroom crashed. Before I close the error window I could see that Lightroom wants to load files from drive F and H too. Is there any way to change all the faulty drive letters inside the catalog file? Nothing is wrong inside the catalog file but the drive letters, the folder structure is the same. So I need to change letter H to F inside the catalog file. Is it possible?

Thanks.