HeapFixer and HeapTool don't do anything in System 7. The system has changed such that these utilities won't be needed. The function HeapFixer and HeapTool perform is done by the new boot code in System 7. The system heap will now dynamically grow as extensions allocate more space.
HeapFixer had value with system software version 6.0.X because INITS would add to the system heap, and the heap filled up. Looking at the system bar in the About box and adjusting the size so that enough space is left over won't work any more.
The system software indicator in System 7 includes a lot more than just the system heap, so it can't be used as an indicator of how much space is currently available. And since the system heap is dynamic in System 7, even during startup, any adjustments made by the HeapFixer and HeapTool utilities will just be overridden by the system.