Thanks for your question.
If you don't have your original CP575 notice that IRS sent assigning your EIN, you will need to call IRS to get a Letter 147C issued to you. The Letter 147C will confirm your EIN. The IRS business help line can help you at 1-800-829-4933. The hours of operation are 7a.m.-10p.m. local time, Monday-Friday.
You may send a written request for the letter 147C but it would be faster to call and request on the phone.
Hope this helps,