Undergraduate changing research field with a deadline I have a friend who is working in the wrong field of physics at the moment (not enjoying it.) They are still undergraduate however and have time to change this. 

They are currently working on a summer project which will soon end. If they leave now it will be time (and a scholarship) wasted on them, because most of the summer project was teaching them the basics of what to do (a 6 week project.) 

They are about to start their final year in undergraduate physics, and in this year the university offers a project based unit, with a similar structure to a summer work project, but with assessment at the end. Students taking this project often use it as a lead in to an honours year at our university, then honours leads into PHD if they get it. 

Although university hasn’t official begun here yet, the deadline to choose a project is fast approaching (March 11). To choose one my friend needs to contact a supervisor in the right field and ask to take the unit under them.
I was wondering if anyone here has experienced or seen anything similar to this before, and what their advice to my friend would be. My normal advice to them would be to take your time to find the right supervisor/field of physics, and work under them regardless of the current work. (After all, they are still undergraduate and are allowed to make a mistake.)

However, due to the deadline for the project choice, it might not be easy to find the right supervisor. Which is why I’m asking online for any advice.
I wouldn't sweat the summer spent.  It was a mistake but better not to extend it.  If you want a rationalization, just go with "at least the 6 weeks taught me what I don't want to do".  

All that said, if you enjoy the work, the group, etc. despite it being laser optics when your interest is NMR (or whatever) I would not feel that you need that this project determines your grad school subfield or project. People switch interests all the time when moving to Ph.D.

After all it is just a year, part time.  Doing anything is better than nothing.  And nobody will expect you to do a Ph.D. in whatever subfield you did a short undergrad project in (or "bachelor's thesis").  IOW, there is a natural breakpoint later.  Consider some people don't even have undergrad research.  So if you like the stuff and just wants to have something for the year, don't sweat it and stick with the known quantity. 

Conversely, if you hate it...bail. In terms of how to find an advisor...go beat the bushes, talk to people, look at websites, etc.  Stat.  And I would just do this exploration now, before ditching the other opportunity (so if you can't find an upgrade, you can stick with the summer topic).

[This seems like common sense, so if there is more to the situation, you need to give us those particulars.]