This is set up from the Company Settings. Navigate here by clicking your initials in the top right corner, then selecting “Account”.
Set up your company profile first. Once that is created, you will see an option to click Edit Defaults. (As shown in screenshot below.)
A pop up will allow you to enter your Tax # and any notes (shown at the bottom of the invoice). By default, these values will now show in all your invoices. Be sure to save your changes.