Well, with an complete installation of MiKTeX (admin mode) I can see the package
amsaddr in the MiKTeX Console:
As you can see I added name
amsaddr (see red arrow in image) and selected to search for it (red circle marked with 1) to get a list of installed packages
amsaddr by MiKTeX.
If you have not already installed that package the + sign in the red circle marked with 2 will be dark and shows you can install this package by clicking on the + sign!
BTW: To get the window I showed you you have to start the MiKTeX Console in the apps of windows, then click on
use in admin mode (because you also have an admin installation) and the click on
Packages I marked in the image with the long red arrow ...
If you did changes in user mode it is possible you have to do that again in user mode ...
Because you gave us no minimal working example (MWE) I can not test if I get the same error message you got ...