If you have stored data on a USB stick or an external hard disk and want to access it with the Huawei P20 Pro, you cannot avoid it via an OTG adapter. OTG stands for "On The Go" and is a service provided by the Android operating system in conjunction with the smartphone's hardware.
The Huawei P20 Pro supports OTG, so you can connect a USB stick or hard drive to your phone and access it with File Explorer. In order for the Huawei P20 Pro to recognize a USB stick, you need an adapter that converts from USB Type C to USB 3.0. For example, you can get such an adapter on Amazon for little money:
This adapter is then plugged into the USB Type C port of the Huawei P20 Pro. The USB stick or hard disk then goes to the other side of the adapter. Attention! With hard disks, an external power supply must always be used, since the smartphone transmits too little power to the hard disk via the OTG port to operate it alone.
You can then access the USB device with any file explorer and copy, move or delete data on it.