If you are looking to evolve the Porygon you just got after completing the main story of Pokémon Sword and Shield’s Isle of Armor expansion, then you will just need to spend a little time exploring the new Wild Area.
Both the Upgrade and Dubious Disk can be found without needing to do any extra side quests or looking for an NPC, but you will need to go to the far reaches of the map.
To grab the Upgrade, which is needed to evolve Porygon into Porygon 2, you will need to head back down to Warm-Up Tunnel and exit towards the Training Lowlands. Towards the left between the beach and the entrance to the cave you should find yourself the Upgrade.
You can also combine a specific set of items together to get one out of the Cram-o-matic in the Master Dojo. Put in a Yellow Apricorn, Big Nugget, Big Mushroom, and Star Piece to receive a second Upgrade.
After you get your Porygon Two, it is time to set out and find the Dubious Disk, which is a bit easier to find once you get a look at the map.
Head South from the Master Dojo and out into the open water before paddling out towards the smaller islands on the outskirts. After dodging Wailord and Sharpedo along the way, you should find a Poké Ball resting on the shores of one of the furthest small landmasses.
Slide up onto the beach and claim your prize, because for heading out that far you got yourself a Dubious Disk and the ability to trade your Porygon Two to get a Porygon-Z.
There is probably a recipe for getting a Dubious Disk out of the Cram-o-matic too, but it is unknown at this time.