Exchanging a gift with Mateo in Pokémon GO can be a rough task if you do not know where to look. Mateo first appeared during the Season called Timeless Travels, as he is part of the A Route to New Friendships special research task. In the first step of that mission, one of the quests that needs to be concluded is exchanging a gift with him. While exploring 1km, spinning 3 PokéStops, and earning candy while exploring with your buddy are all pretty straightforward and easily accomplishable, giving a gift to this new NPC is somewhat mysterious, especially if you have not completely dived into the the game’s new mechanics.

https://screenrant.com/pokemon-go-mateo-gift-how-to-exchange-route/