You can change the nr of decimals of some data types by creating an extension. This is only possible on supported data types that don't extend any other datatype. So you must find out the data type of this field, and find the root data type for it, and see if it supports changing nr of decimals with extension.
This is a rather new feature, and new data types are enabled for this feature, so the newer app & platform version you are on, the better.
