I think the strongest proof will be the approval of your application for change of status in the US. Since your status is already approved and you have a valid I-20 (I don't know if you have to surrender your I-94 when flying out of the country). You must get your passport stamped with a new visa before entering the US, however, the following documents will make the process very easy and visa is (almost) guaranteed. 1. Valid I-20 You must a new travel I-20 with a signature of your international advisor. If your I-20 is more than one year old, never go out of the country with your your original I-20. Before your international office issues a travel I-20, they need your bank statement and every other document you normally would present at the consular office in Nepal. 2. Notice of Action (I-797) that your change of status from B1/B2 to F1/F2 has been approved. 3. New I-94 after change of status Please follow every steps prescribed by your international education office.