Go to the required flow. The bottom of the page will contain 4 tabs, click on Runs as highlighted in the below image. This will show you the run history of the flow.

The run history will appear as shown in the below image. Click on the date of a run that you want to view.

Use the scroll on your mouse to zoom in the flow and investigate which step the error occurred in. In the below example, there were 10 errors coming from the Salesforce destination step. To view the errors, click on Total Record Errors.

The below page will appear with record number where the error occurred together with the error message. To view the detailed error message, click on a record number hyperlink as highlighted.

Illustrated in the image below is the detailed error message in the record, the current record that got the error and the original record. Click on the Record tab to view how the record looks before the step. The Original Record tab will show the record looks from the parent source step.

Click on View RunEvents as highlighted in the below image which is the history of a run.

Click on the eye icon as highlighted and illustrated in the below page to view the log for each run event that occurred. You can expand the error message on the right side of the page to view what the error is.