To act dishonestly in order to get something for yourself, or to change something dishonestly, especially to your advantage. (Cambridge Dictionary)
An act of defrauding, cheating, or falsifying. (Oxford Dictionaries)
If someone fiddles financial documents, they alter them dishonestly so that they get money for themselves. (Collins Dictionary)
If you fiddle with an object, you keep moving it or touching it with your fingers. (Collins Dictionary)
A device (such as a slat, rack, or light railing) to keep objects from sliding off a table aboard ship. (Merriam – Webster)
NHS being pressured by government to “fiddle the figures” to make finances seem better, documents reveal.