Blissey is available in Pokemon Sword and Shield's first DLC pack the Isle of Armor.
Obtaining this new Pokemon is not as easy as you might think. Here's our guide to evolving Chansey and getting Blissey.
Friendship
Friendship is a mechanic within the Pokemon series that does not have an actual meter or gauge, but it is one of the most important measurements for some Pokemon.
In order to increase friendship for your Pokemon, all you have to do is to keep the Pokemon in your party and make sure it does not die! Letting a Pokemon faint will drastically decease your Pokemon's friendship LVL!
Chansey's final form is Blissey, which is essentially a bigger and fluffier version of Chansey. In order to evolve Chansey into Blissey, you are going to need to LVL up your Chansey with high friendship!
This shouldn't be a problem for you, just make sure Chansey does not faint!