Azure DevOps - use GUI instead of YAML to edit build pipeline

There is a link in the Create New Pipeline blade. Click on the "Use the classic editor" link and voila you will get the GUI to work on!

for a pipeline thats using yaml - no. you can only configure it in yaml and you can not switch back to UI experience.

If the pipeline is UI - it will continue to work as it was working.

You won't be able to use the GUI as it did in the classic editor, but you can click the hyperlinks above your yaml tasks to pop the properties window on the side pane. It's basically a 'designer' for your yaml blocks, so you don't need to 'memorize' anything per se.