QB Issue Resolution:

you can not

all you can do is print the BOM, one at a time, and export that screen to excel

google for ccrqbom – third party utility for assembly items

Resolution for Issue 'How do I output the BOM table/data for all Assembled items to Excel?' available: Yes (Solved).
Source: Intuit Community forum.

How do I output the BOM table/data for all Assembled items to Excel?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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