Having a growth mindset is so incredibly important in science (and in general)! I intentionally spend four to five days at the start of the semester explicitly teaching students about growth mindset in science. You could integrate any simple STEM activity into the theme, but I love asking my seventh grade students to fit their entire bodies through the center of an index card using only a pair of scissors. You can imagine the looks on their faces when they hear what I've asked them to accomplish.
Throughout the lesson I build in hints to keep them encouraged, and as students begin to figure out how to accomplish the task their energy becomes contagious. Students begin encouraging each other to succeed and are proud to show off when they succeed themselves.
I usually end the class with a reflection on how things seem impossible at first, but when you learn how to do those things they become easy.
Here's a link to a tutorial on how to fit yourself through an index card: https://www.youtube.com/watch?v=71bzxv0032s