Hi @Raphael_Teodoro_Silv (and @lincoln19922)!
In this case it would be better to use Issue link field dimension and not JavaScript custom field in advances settings as it contains getDocument() and therefor could affect Jira performance and be much slower.
See more info here - https://docs.eazybi.com/eazybijira/data-import/advanced-data-import-options/issue-link-field-dimensions
The code in advanced settings for getting Epic labels is this:
[[jira.issue_link_field_dimensions]]
name = "Epic Labels"
source_dimension = "Label"
issue_id_column = "epic_id"
group = "Linked issue dimensions"
This customfield will appear in data import tab Additional options -> Issue link field dimensions.
best,
Gerda // support@eazybi.com