[John Murdock]

1) Open the preferences file and look for the entry named “enableContentRecovery”, change the value from 0 to 1. This turns on the feature.

2) Launch Illustrator and choose “File>Open”. Select the file from which you wish to recover the roundtrip information.

3) Click “OK” while holding down the command, shift and option keys (control, shift and alt on Windows).

Or if all these steps couldn’t aid you, try Illustrator Repair Toolbox. You may download it from here: https://www.illustrator.repairtoolbox.com/