Type the time support gave you, pick the zone it came from, and read it back in Eastern. Both formats work: 3pm, 3:15 PM, or military like 0130 and 15:30:00. Paste something like 3pm CST and the zone gets picked up for you.
Times marked EDT or EST are the same Eastern clock — the label just changes with daylight saving, which is why the date field matters.
If support writes “EST” in July they usually mean Eastern time generally, so leave the zone on Eastern (ET). Use the fixed-offset options only when you know they meant a literal standard-time offset.