When you need to find a synonym for the term "fixing up on," there are a number of alternatives that you can use to express this concept. For example, you might consider using words like repairing, renovating, refurbishing, sprucing up, or enhancing. Each of these terms conveys a slightly different nuance, depending on the context in which they are used. For instance, repairing might suggest that something is broken and needs to be fixed, while enhancing might suggest that something is already functional but could be made better in some way. Ultimately, choosing the right synonym depends on the specific situation and your intended meaning.