Money exchange

Usually in you can exchange money in Tokyo just by going to any of the big branch banks.
The first time I came, I just went to Shibuya, there was a big Mizuho bank there near the famous crossing and I exchanged there. It's a blue bank in case you are wondering, and I believe it's the best for exchanging.
Here's the address of the Shibuya Branch and also a list of all locations of Mizuho banks in tokyo: https://shop.www.mizuhobank.com/b/mizuho_en/attr/?start=6&kencode=13

The post office may exchange it too, just look for JP bank or JP (Japan Post).

Also, there's a money exchanging place just outside of Yodobashi Akiba in Akihabara.
https://planetyze.com/en/japan/tokyo/yodobashi-akiba

I hope this helps :-)