Deleting old WhatsApp messages on iPhone

I am using

WhatsApp Business on my iPhone 12 and have approximately 150 000 conversations

with more than 1 million messages in total. 

WhatsApp is not working properly anymore, it freezes etc due to the sheer

volume of messages.  I already deleted

all large messages by using the “Manage Storage” function, which only helped

for a short while but is not the solution.  My phone still has about 180GB available

storage.

How can I

bulk delete all messages (not conversations) older than, let’s say 4 years?

[Re-Titled by Moderator]