How to add variables to api calls in blazemeter to load test GUI

I have been currently using jmeter for my load testing, this includes registering a user and using an authorization token and things of that nature, this includes using a json extractor/header extractor etc for each run as these variables would be dynamic and change.

This is working fine but im having issues when im trying to use the blazemeter gui tests. Im able to record the flow using the blazemeter extension but cant seem to find an option to load the jmeter script and combine it with the ui recording so i can run the GUI tests for multiple users.

I have already been able to add the jmx file to blazemeter and run it there but again i see no option to edit this within blazemeter or add it to any GUI tests?

All i want to do is assert that pages are loading within a certain duration but can seem to get this working with the apis and GUI.

Any help appreciated