For doing this you can select the file in Windows Explorer or from the Open dialog in Inventor, right-click, Design Assistant.
In Design Assistant, Manage view, in the upper side, select the file, if it is not selected yet.
In the lower side, select the boxes corresponding to types of file where the file has been used (or, in doubt, select all the boxes.)
Then, click on the button, Find Files.
Unfortunately, if you get an error, trying to open the file in Inventor, possibly you will get the same error or similar, opening the same file in Design Assistant.
In any case, I hope this could be of some help.
In Design Assistant, the derived part source files will be listed in the tree in the Properties view - no need to use the Find Files function. If a derived file is missing, you should get a dialog box with the option to Continue. The missing files will be marked with a question mark or broken link icon. You may need to hit Refresh to get these to appear.
You have inserted Part1 in some assemblies and derived it in some parts.
Now, you want to know in which assemblies and parts, Part1 has been used (or, at least, I think this was the question).
Well, if this is the case, you need to follow the steps I’ve shown above in Design Assistant.
Unfortunately, if Part1 is corrupted this is not going to work.
In your original post, you said 'an error comes up'. I t would be helpful if you could give more info about the specific error message.
The way I read the question, he's asking about the derived part/assy references inside a part file. AFAIK, the are no 'where-used' references stored inside part files.
Did you check if in the OldVersions folder of your project there is a previous version of this file that can still be opened?
Thanks and regards,