Hello everyone. A nice topic to start posting here.
For Greece, Fani Tzeli will be competing in tae kwon do, along with the rowers. Tzeli won bronze in 2018.
I'll try a different approach and I'll go by sport.
In swimming, there are a lot medalists from 2018, who are going to Tokyo. I'll name a few. The events mentioned are those in which they got the medal in 2018, not (necessarily) the ones they are swimming this time.
Hungary
Milak 200 free gold, 400 free gold, 200 fly gold, 100 butterfly silver
Kesely 200 free gold, 400 free gold, 800 free gold
Australia
McKeown 50 backstroke gold, 100 backstroke silver, 200 backstroke bronze
Hodges 100 breaststroke silver
Russia
Minakov 50 butterfly gold, 100 butterfly gold, 100 freestyle gold
Kolesnikov 50 backstroke gold, 100 backstroke gold, 200 backstroke gold
Italy
Burdisso 100 butterfly bronze, 200 butterfly bronze
Ceccon 50 free gold, 50 backstroke silver, 100 backstroke bronze, 200 IM silver
De Tullio 400 free silver, 800 free bronze
Czech Republic
Seemanova 50 free gold, 100 free gold, 200 free bronze
Israel
Gorbenko 200 IM gold
USA
White 200 backstroke bronze
France
Duhamel 200 IM bronze
Canada
Knox 200 IM bronze
Probably, there will be more who will compete in relays, plus those who didn't win a medal back then, but will swim in Tokyo.