First, look at this page to see if the app is listed. If it is, copy and paste the activity name into the Activity String box on this form.
If the app isn't listed on the aforementioned page, you'll have go through the following process. Note: adb, as well as the appropriate drivers for your device, must be installed on your computer first.
adb logcat ActivityManager:I *:S
I/ActivityManager( 2453): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.metago.astro/.FileManagerActivity bnds=[5,415][115,533] }
It is a bit of a hassle to go through this process, but if you do it, the icon creation process will be expedited.