The picture is not clear enough to see detail, are you sure that it is not a seed or a piece of food that is stuck there? If not, from the color of it, it may be a small lipoma, best to have it looked at by an avian vet.
Truly, the very BEST advice anyone can offer you is to take the time to read ALL of the stickies throughout the various Talk Budgie forums as well as the Budgie Articles we have posted.
(Stickies are threads “stuck” at the top of each forum sub-section)
These are great resources for Talk Budgie members and have a wealth of reliable information which will assist you to learn the best practices in caring for your budgies for their optimal health and well-being.
I also second the advice above by my fellow staff members. Do you have any updates on your budgie? Is the spot still there?
Meanwhile, please be sure to read through the links provided above to ensure you're up to date on the best of budgie care practices. If you have any questions after doing so, please be sure to ask as we'd love to help.