I cleaned up the application a bit and the code a bit:
You must login or register to view this content.
\Instagram Multiple Username Checker\Instagram Multiple Username Checker\bin\Debug\...
.exe and theme.dll are the only two things you need from it to get it to work. There is no icon, simply just put it into a folder and run it.
I got bored.
Anyways, the same is with anything else, there is no need to compile it since the source is given to you with a build already in it.
Edit: It looks like I broke it when I tried to compile as a release (lol, reason why I hate custom themes w/ winForm). Anyways, the source is there, the application inside still works. Modify the two ListBoxes named "input/output" to "inputBox" and "outputBox" and just copy/paste my code. Also rename the form to "MainForm.cs" before doing anything. You can then compile it like normal.
Won't bother fixing it, have fun.