(solved) How to see a multistore in test setup??

Okay so I am working on v3 in a subdirectory on my hosting server and there are a few things I need to make sure works in 1 store but not another. Problem is I cannot figure out how to see that temporary 2nd store front end without wrecking my live stores.

I have live stores in root which is v2 (mystore.com)
and v3 development store in a subdirectory mystore.com/v3test/ for example

I tried to set up a temporary subdomain for store2.mystore.com/v3test/ (with root set to mystore/v3test/) but when I try to go to the front end I get "page not found" from my v2 store. Not seeing it's pages or template either (different logo set up in settings).

Any idea how I can do this? I want to set up the colors/styling/menu etc for each of my 21 online stores so I can just enable them and assign theme/etc once I move it to root to make it live. I can set up layouts, etc, but cannot see them to make sure they are the way I want them to be.

These are all quite complicated server setup questions, do you have cPanel?

actually my web hosts were able to set it up for me so thanks @evolve! I'm working thru the multi store designs now one by one. thanks!

Hi,
I have setup an test or demo for Multistore also I have made a video showing just that..
https://youtu.be/kRoFC48RKAY