In the SCI Resource Viewer, open QFG4 and expand the Script folder. Select 18.scr, click File, Extract. Save as 18.scr, the default. Now do the same with 18.hep in the Heap folder.
Unnecessary explanation of why you need to extract those files, feel free to ignore: another script in the game checks for the presence of the file 18.scr and enables access to the debugger if it's there. The debugger itself is script #18, already there in the game but inaccessible. Technically you only need to extract the script, not the heap.