Hello @Jan Sękara
As @John Funk said, you will need to first make sure that the field is available in the issue type for the linked task, and visible on the screens for that issue type.
Then, you will need to copy the field value from the Epic to the linked task. You can have a dynamic reference that shows the parent Epics value in the linked task issue, but you can copy the value from one issue to the other using the Automation feature. Here is the home page for information on that feature.
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