We all need extra storage and as WhatsApp tends to automatically download all its data into the internal storage of your phone, it is best to move it to the SD card. You can do this in two ways:

1. Using a USB cable and a PC
2. Using a file manager

The easiest way is by using a file manager. All the actions will be performed on your phone.

No matter your phone brand, you should have a pre-installed file manager app, which allows you to examine all your files and their locations. Just open your app drawer and look for one. After this, follow these steps:

1. Look for the Whatsapp folder on the root of your internal storage and open it
2. You should see two folders: Databases and Media. Open the Media folder
3. Here, you have multiple folders, one for each type of media you have received through Whatsapp
4. Select the folders (or just the files) you want to move to the SD card and a new menu should appear on your phone, including an option called “Move to”.
5. Tap on “Move to” and select the folder’s/files’ new destination. In this case, the memory card

I hope it helps and frees some of your phone's internal storage.

https://www.unlockunit.com/blog/move-whatsapp-data-sd-card