Copying WhatsApp chat history to new Android

There have been many questions asked and answered on this topic but unfortunately I’ve not found one that addresses my issue.
I have read that to transfer the WhatsApp chat history to a new phone it is necessary to first back up the chat history from the old phone (before removing the SIM) to Google Drive. Unfortunately I didn’t do this. I moved the SIM from my old to the new, installed WhatsApp and registered it with the old number, so losing all my chat history.

I assume that my chat history is still on my old phone but if I run it with a different SIM, WhatsApp presents me with the welcome screen and I have no way of accessing my chat history (I have not tried registering WhatsApp on the old phone with an new number). So I now have a chat history on both my old and new phones.

Is there any way to access the chat history from the old phone and combine it with that on the new phone.

Suppose I temporarily move my original SIM back to my old phone and get WhatsApp running again with the old number, will my chat history be restored? If so, I am thinking I could then do the Backup to Google Drive and then somehow combine the two histories on the new phone