If you already have an active Boost serviice you can just put your SIM card into any compatible phone and you should be good to go.
If you need a SIM of a different size, try have a chat with Boost Support on 1258881 or here.
(Note: if you are actually with Boost USA you should go here.)
I would love to assist you but I am unsure as to the nature of your enquiry. Let us know some details about the issue you need help with and we will do our best to get an answer for you.