You can mix different antifreeze brands and coolants together as long as the coolants are the same colors as each other.
What you can't do though is mix green and orange engine coolant together as it can create a gel like substance which makes it hard for the coolant to go through your engine.
Although it's better to just use the same brand of antifreeze for your vehicle all the time so you know it's getting the correct mixture so your engine won't freeze and crack or overheat.
But as long as the engine coolant is the same color as the coolant that is already in your vehicle then it should be fine to mix the coolants together if you can't find the same brand of coolant that you normally use.