You must know that Gmail has a feature called "Select all conversations" that allows you to select more than 50 emails at once and then delete them. Here are the steps that you have to follow:
Open your web browser, go to Gmail, and sign in to your Gmail account
Use Search Filters if you want to search specific emails
Otherwise select all conversation
Click on delete the selected emails
Empty the trash
That's it
In case issues then visit: https://emailspedia.com/how-to-delete-o ... -in-gmail/