How to boost 12V DC to 24V DC?
The two basic methods are to use a crude voltage doubler, or a fairly simple boost switching regulator. If you cannot build one from scratch parts, a pre made module can be purchased on good electronic sourcing sites like Digikey, Farnell, etc, or less quality sites like eBay Amazon etc.

Or buy a 24V supply. A cheap wallwart can be found on the same sites, or a thrift shop.