This is the 371st most frequent Icelandic word.
ykkur
"Ykkur" means "you" (plural, accusative or dative case) in English.
In this sentence, "ykkur" is the object pronoun addressing a group of people in the second person plural.
Ég sé ykkur á morgun.
I will see you(plural) tomorrow.
The word "ykkur" here is used as the indirect object pronoun indicating the group benefiting from the action.
Við höfum safnað fyrir ykkur.
We have collected for you(plural).
Here, "ykkur" is used reflexively to address a group of individuals instructing them to perform an action on themselves.