1) You will need to open up your Merchant Centre account;
2) Click on the cog in the top toolbar as shown below, then click on Account access:
3) The following should then be displayed. You need to click on Add user:
4) Once you press the plus to Add user, you’ll be greeted with the following:
In here, please add the following email address: firstname.lastname@example.org
Then click Add user to save this information.