I try to use my RPi3 and the RC522 and a touchscreen display as well so i need to put my RC522 on the auxiliary SPI1 right ? How can I do it ?
There's two ways to add a second SPI device to the board. You can add it to the first SPI bus and use the second chip select and access the device at /dev/spidev0.1, or you can add an device tree overlay to access the second SPI bus available on the 40-pin header. spi1-1cs, spi1-2cs, and spi1-3cs only differ in the number of chip select pins available, if you only use the two devices listed in the question spi1-1cs uses the fewest pins.
The biggest thing that comes to mind is that you can only talk to one device per bus at a time. If you use both busses you use up more pins, but managing the devices is easier. If you put both devices on one bus there's a chance you'll have to wait for one to finish a transfer before using the other. How important that is varies a lot by project depending on if you need the pins for anything else, and if you have any bandwidth or latency requirements when talking to the devices.
Here's a tutorial on how to do it: