I was an enormous fan of Pokémon GO for several years, zealously playing no matter where I was. It spurred me to do interesting things like visit parks in my area to which I had never been, to capture the Pokestop. I joined in legendary battles. I recall captuing MewTwo at a local park with about a dozen other players. I'd been a player of Niantic's earlier game Ingress, and thought of Pokémon GO as a newer, shinier take on the concept.
As happens, my interest in catching Pokémon waned and eventually stopped by the summer of 2019. We went to LEGOLand and there is exactly one Pokémon screenshot in my photos, in what was surely a target rich environment. Emailed entreaties from Niantic to come back started a couple months later.
I knew that location data was the main economic reason for the game's existence. I wasn't especially concerned about it at the time, I felt confident that my visits to parks and monuments and fountains wouldn't be something to be concerned about.
That was then, this is now. The world seems more threatening, and Niantic's announcement of the sale of its games and location data to Scopely, which is owned by the Saudi Arabian sovereign wealth fund, is enough to trigger my spidey sense.
One can request deletion of the account and associated data from within the app if still installed, but it is not necessary to reinstall if already gone. Niantic has a request form to delete a Pokémon GO account. If you don't remember your account name, search your Inbox for the pleading entreaties to come back to the game — it went on for years.
After submitting the deletion request, Niantic sent an email requiring that I reply with a code to confirm the deletion within 30 days. Right now I'm trusting that they will actually delete the data: one person's information is valueless, there isn't a reason to lie about doing so.