There are a couple of ways to go about this. My preferred way is to create an Interface BP, and give at a Get Value/Set Value function. Implement that interface on your object 1. In object two, get a reference to object 1, and call the function via the interface. That works great if it is something that you will be using for a lot of different objects of similar types. I.e. Enemies, lights/switches, etc.
Option two is to get a reference to Object1 in your Object2 BP, and use a cast to node to get/set the variable directly.
The hardest part is getting a reference to the correct object. That can be done in a number of ways, such as collision detection, getting a reference from your level/game instance BP, Get All Objects of Class, Get all Objects with Tag, or setting it via an On Touched/On click function. Without knowing exactly what you are trying to do, and what the scenario is, it is hard to say which method would work best for your situation.