How do I convert 5 V to 9 V?
You need a thing called a &quot;boost converter&quot;.  If you were a product designer you'd probably design one onto your board, but that's a job for the experienced -- if you need to ask, it's probably beyond you.
You can get cheap unreliable ones from eBay or hobby electronics sources, or you can get reliable ones from distributors.  Basically, if it doesn't have a full data sheet, and you don't have a route to send a defective part back to the vendor, don't trust it.
Careful shopping is in order.