How to mine on a specific GPU?

I have only ever used Nicehash. Now, I want to start mining RVN outside of Nicehash. My rig has two gpus, one Nvidia, and one AMD. I may very well add a third gpu to it with an upgraded or a 2nd connected psu. For now, I just want to mine with one card. How do I select which card is mined with? And how can I prevent any errors using a Nvidia based mining application conflict with my AMD card? And likewise, how can I use both cards without errors? On Nicehash, it runs smoothly, identifies the cards and applies the appropriate mining application. But in all the FAQ guides on how to start mining RVN, none address how to select which gpu card to be used, or how to use multiple gpu cards (and from different architectures)