So, don't worry, I will explain How to Repair Internet Download Manager (IDM) [Fake Serial Number Internet Download Manager].
First, open your Internet Download Manager where installed. If you are using default installation, your directory in C:\Program Files\Internet Download Manager. For example like this picture
Third, open the file using text editor, for example I'm using Notepad . Click right the file => open with => choose Notepad++. After opened, write anything and save. For example look at the piccture below.
Fouth, copy and replace the file (IDMGrHlp.exe) in its original place of IDM installation. Enjoy it
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