HELP! How do I resize assets automatically, help me to become a professional :"P

Hi People, 

So i've been working in XD lately, very nice software.

I can't seem to find any good approach for using/resizing icons/symbols. 

When I make a design. I use a square icon placeholder which is an asset (in my asset list) So I can later swap in the right icons from my asset list easily. 

But when I resize the icon placeholder, and later swap in another icon. The new icon keeps its original size. How do I let the icons resize to the new size? 

Now I do it like so: (this doesn't work) 

1. Here you see the square (placeholder) I resized it manually (the little square underneath it) then I copied both to display what goes wrong.

2. I click/dragged the icon I want on the placeholders location, first the same size. This goes well! 🙂

3. Now I want to do the same for the resized placeholder, but the icon stays the original size. 

I would like to learn how to approach this correctly. 

Or how should I create this professionally, if the way I approach this isn't correct/as designed. 

Thank you all in advance!

Olmo