Does your garage by chance have aluminum insuation or other thick materials such as brick or concrete, separating the signals from in the garage, to the rest of the house? If that's the case, you've essentially got a faraday cage. The most effective way to fix this is to use a Wired connection. Using a booster on the other end of the garage wall to try to fix this won't do much besides degrade the spectrum in your area further, and speeds won't be too good.
You can get a Wired connection through Powerline, by runing CAT5e/CAT6a cabling, or by using available Coaxial cable via MoCa. From here, you can install another Wireless access point or simply wire up the devices you need.
If you could describe where your ONT is located, and how you got a Wired connection to your garage when you re-located the router, we can help get this squared away. For now, leave your router in the central location it's located at, where it's likely already giving optimal reception to the places where others use it, except for your garage.