You're going to need to provide a lot more information than that. Things like:
-Condition of the firearm (cosmetic and mechanical)
-Who was the soldier?
-Do you have any physical proof that this soldier had it?
-Is there any evidence the soldier actually carried it?
Pictures are often helpful as well. You can post them to Google drive and link them, or post directly.
The people on this forum are very knowledgeable and usually very helpful. However some information is requisit.
I've seen fosberries go north of $7k, but those were presentation pieces. A rust bucket might be worth a couple hundred.
As far as how to sell, there should be a sticky explaining restricted sales. You can request access and sell in the Pistols and Revolvers section on the EE, use an auction or take it to your local gun store. If transporting, ATTs are obviously required. All of this assumes that it is registered to you. If it's not registered, you will have to do that. Hopefully you have enough time...