Assign User to Site (without Department)

Assign User to Site (without Department)

I am trying to give the users on my instance an association to a site, and while I know I can give users sites through departments, for my use case, most users can't really be said to belong to any definable department (and in most cases such a department wouldn't really be limited to one site anyway). Is there a way to set a users site directly?
Thanks!

(And for context I'm using version 15240 On Prem)

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