ñ Ñ
its option n on Mac, on windows its unnecessarily complicated, but here goes.
For Windows you need to hold down ALT while typing the appropriate number code on your numeric keypad to create characters with tilde accent marks. (It has to be the number pad, the numbers at the top of the keyboard won't work.)
For the upper case letters:
à 0195
Ñ 0209
Õ 0213
For the lower case letters:
ã 0227
ñ 0241
õ 0245
It is overly complicated like i said, so its probably easier to google it and copy paste, but there you go.