You can define your selection priorities in this menu option for the automatic selection of a BOM usage:
The allocation of applications ('INST' in the standard system) to selection IDs ('03' in the standard system) is dealt with in the chapter 'Defining application-dependent selection IDs'.
Find out the BOM usages that you are using for plant maintenance. If you are only working with one usage ('04' in the standard system), you only need to check the default settings.
Define the BOM usage priorities.