1. Salesforce Help Documentation: Ground a Prompt Template with Salesforce Data. In the section "Ground in a Record's Data
" the documentation states
"To select the fields that you want to ground your prompt template in
create a field set on the object... From the object management settings for the object that you want to use
go to Field Sets
and then click New."
2. Salesforce Trailhead: Prompt Builder Basics module
Ground Prompts with Salesforce Data unit. The documentation explicitly notes
"To use a record snapshot
you first create a field set on the object that you want to ground the prompt in. The field set determines which fields are available to the prompt template."