Configure GPIO pin for infrared interface (IRTIM) of STM32F030x4/x6/x8

I have a problem for use infrared interface (IRTIM) of my MCU. When I saw in Reference manual I could find this:

Now, when I search for find GPIOx_AFRx register, I cannot find this register in reference manual.

Where is it?

The actual register isn't named GPIOx_AFRx, the "x" is a placeholder for other designators.
If you look at sections 8.4.9 and 8.4.10 (PDF page 128) of the document you linked, you'll find they deal with the GPIOx_AFRL and GPIOx_AFRH for the low and high registers, respectively.