If your inventory is full you can go back to snowdin and into papyrus s house to get her letter assuming the inventory has a space left.
Slide the letter under the door undertale.
Undyne letter ex cannot be thrown away or sold at the tem shop.
Jump back on the ferry and go back to the hotland with dr alphys lab.
Unfortunately undyne didn t sign it so alphys will think this declaration.
You sure you have the letter.
Undyne gives the protagonist undyne letter ex as a replacement if the protagonist throws the original letter away.
If you have the letter the entrance to the lab should be closed and interacting with it would let you slide the letter under the door.
After the protagonist delivers the letter alphys engages in a date with the protagonist.
The door should be closed so you miiiight ve encountered a bug.
Head back to mtt resort and undyne will call with a favour to ask.
Get the ferry from hotlands to snowdin village and go to papyrus s house and undyne will give you a letter to deliver to alphys.
All you can do is slide the letter under the door.
Undyne s letter is a letter that undyne gives to the protagonist to deliver to alphys in a true pacifist route.
Go to hotland and into the lab door slide undyne s letter under and complete the date with alphys.