Having a high number of open chats can be detrimantal to the performance of your WhatsApp number, for this reason we recommend to keep no more than 1000 open chats per WhatsApp number, and ideally around 600.
If the number of open chats is slightly higher, you can just activate the automatic chat clean up tool and the system will do it automatically.
Please refer to this article to learn more about it.
On the other hand, if you have several hundreds or thousands of open chats, the system will not be able to eliminate the chats and you will need to do it manually. No worries, though, keep on reading to learn how to do it.
If you have to eliminate a high number of open chats, you want to hand pick the ones you want to delete or you want to delete them all, you can do it manually from WhatsApp application in your physical device. Please find further details on WhatsApp help pages: