Normally there are actually two ways to reinstall WhatsApp without losing your chats -
Using a local backup
Using Google Drive
Most tech savvy people would actually use the Google drive feature because it's easier but it doesn't guarantee you will get your last chats because WhatsApp automatically backs up chats by 2.am and if your data connection isn't turned on at that time, your chat backup would not be uploaded to Google Drive only the local backup would be kept and if you don't know how to restore it properly you will lose your chats
So without further ado lets get started on how to restore your chats on a new phone using a local backup.
1. Install Xender On Both Phones Then Open Xender on both as well and connect the phones.
2.Go To File Manager > WhatsApp > Databases
3. Mark And Send The Databases Folder To The New Phone then close Xender
4.Install WhatsApp on the new phone but don't launch it yet (If you have already launched it long press the WhatsApp icon till an info logo (i) comes up then click on it or drag the icon towards it, this will vary depending on the launcher you are using. Once you do that click on the clear data option)
At this point you are done with the old device. Let's set it up on your new device
5. On the new device Go To Your File Manager > WhatsApp > Databases then delete the Databases Folder
6. Go To File Manager > Xender > Folder
7. Copy The Databases folder and go to the WhatsApp folder and paste it there
8. Launch WhatsApp and continue the installation process
9. WhatsApp will detect the backups them restore your chats for you