You must use "risers". The risers are so you can install the gpu anywhere u want, instead of plugging it straight onto the board. Basically it's just a pcie extension which allows more room/freedom

You can also try pcie splitters, but I dont know about them. They split your 1 existing pcie slot into 4 slots, so you can use 4 gpus. You then plug the risers to the 4 slots.

Splitter: https://www.amazon.com/dp/B092R64W2V/ref=cm_sw_r_awdo_D760PJB8K2RHM2X3ESJX

Risers: https://www.amazon.com/dp/B08X4BGKJP/ref=cm_sw_r_awdo_H4NG6QZC6GZD4VC02KCD