Method #1 : Regular trade in game (one by one) via Link Code
Things you need:
1- Nintendo online Subscription
2- Pokemon Scarlet or Violet
3- Prepare 27 Unwanted Pokemon or Eggs ( anything you don't want )
Method#2 :Not Available
All Starter Pokémons :
Bulbasaur / Charmander / Squirtle / Chikorita / Cyndaquil / Totodile / Treecko / Torchic / Mudkip / Turtwig / Chimchar / Piplup / Snivy / Tepig / Oshawott / Chespin / Fennekin / Froakie / Rowlet / Litten / Popplio / Grookey / Scorbunny / Sobble / Sprigatito / Fuecoco / Quaxly