As announced this morning on CU Boulder's Temporary Remote Course Instruction page:
In recognition of how COVID-19 is impacting our students, we are extending the deadline to receive a 60% rebate to Sept. 29. Students who choose to take a leave of absence or withdraw from classes for the semester can work with the Office of the Registrar on the process for withdrawal or for taking a leave of absence. Students receiving financial aid through CU Boulder should review the Office of Financial Aid's withdrawal policy and contact Financial Aid for individual questions.
For step-by-step withdrawal instructions, see Withdraw from the Semester.