Assuming you're using Trados Studio 2019, you can find it here:

C:\Users\[UserName]\AppData\Roaming\SDL\SDL Trados Studio\15.0.0.0\AutoCorrectDictionaries

Now, if you really want to edit the AutoCorrect entries, I'd recommend:

1. Follow the usual procedure in Options > Editor > AutoCorrect:

Otherwise the risk of corrupting the file is high, really high I'd say…

2. Use AutoHotkey, an external application. Then you can edit the entry list without ruining your AutoCorrect options. Please read this blog about how to extract your Office AutoCorrect entries and use them everywhere: https://multifarious.filkin.com/2013/05/31/autocorrect-for-everything/

Thank you, Jesús.

I just export my autocorrect file, amend it and then import it back. No matter where you save the export file.
By the way, this allows you to add entries that you can't add through Studio interface.
For example, there is no way to add an autocorrection pair for thin space (correct me anybody if I'm wrong). You can type it by Alt+8201 somewhere in text editor and then paste it but the 'Add' button won't be activated. The export/import workaround allows you to achieve this task.