if you didn't get your first choice in module enrolment
Most of the time, you're able to get your first choice when you're choosing your modules. However sometimes the modules you want may be full.
Because the process is first come, first served, some courses can fill up within minutes of them being open. If you've missed out or unhappy with what you've chosen, there's a number of things you can do.
Speak with the school that teaches the module
Some schools (not all) have a waiting list you may be able to join. People change their mind, and may decide to do something different. Find out who to contact for module enrolment
Regularly check back during the time module enrolment is open
Because some people may change their mind, it's worth checking back in the module enrolment section - if a place has become available you will then be able to enrol on the module. However as Schools run waiting lists, it's still worth checking with the teaching school to confirm you've got a place.
Wait until the discovery modules are released
Sometimes when discovery modules are released people may change their mind. Again, keep in touch with the teaching school. It's also worth doing your research before this as there may be modules that you'd like to do then.