Hi,
Ketones tautomerizing to aldehydes is an overall process that you only really see for sugars as they need to have an alcohol alpha to the ketone for this to work.
I have drawn an example here, but essentially what you make is an enol that has two alcohols - this can tautomerize two ways, back to a ketone or to an aldehyde - in this way, you can shift where the aldhyde and ketone are.
https://ibb.co/Cnppcgb
Please let me know if this is unclear.