Max available quantity can be set in bulk in two different ways.
1. Bulk Edit tool
This guide explains how to use the Bulk Inventory Edit Tool. Max Available Quantity is an available attribute within this tool: https://support.ecomdash.com/hc/en-us/articles/360005125252-How-do-I-use-the-Bulk-Inventory-Editor-.
2. CSV file upload
Max Available Quantity can be set in bulk through a file upload. When building your import format, be sure to define your storefront and use the attributes SKU Number and Max Available Quantity. This guide explains how to update information via file upload: https://support.ecomdash.com/hc/en-us/articles/215291023-Update-Information-through-a-File-Upload