If cleaning the switch doesn't restore it to full function. You'll have to disassemble the toaster oven and replace the switch (SW 15 on the circuit board).

A fairly common 7x7mm 6-pin DPDT (dual-pole-dual-throw) switch will work as an acceptable substitute.

A full writeup is available here: https://fixitclinic.blogspot.com/2016/12...

For even more backup information see https://uspirg.org/blogs/blog/usp/troubl...