Instructions
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If you need to manually upload a checklist item, you can from the application checklist on the application record. .
Step 1 - Click on the checklist item that you want to upload and then select view record.

Step 2 - From there you will be taken to the checklist item record page. Near the top left click ‘Upload File’ to upload a file from your computer.

Outcome
The checklist item file is successfully uploaded and attached to the checklist item record in Salesforce.