Click on the Bookbot avatar on the right of your screen. You will see four options, click on the bottom one which is blue button and shows two arrows going around in a circular motion.
The profile you are currently using will be displayed in the centre of your screen with two purple arrows underneath it. Two switch profile, click on the other profile which you would like to use.
The avatar of the other profile will then move to the middle. To confirm if you have switched profile, you should see the two arrows underneath the other Bookbot avatar now.