How to make Gmail your default mail client
When you click on an email link on a web page or email message, your computer will open a new compose window with the email address populated in the To: line. The program used to compose the message is determined by the default mail client for your computer. To make Gmail your default mail client, please follow these instructions.
If you use more than one browser you will want to follow the instructions for each browser.
Follow the latest instructions from Google at https://support.google.com/a/users/answer/9308783?hl=en