Disassembly Xiaomi Mi Smart Band 4
Remove the band from your wrist, hold on to each end and pull on the wristband until you see a small gap between the fitness tracker and the wristband. Use your finger to pop the fitness tracker out of its slot from the front side of the wristband.

https://manuals.plus/_mi/mi-smart-band-4-user-guide#ixzz7rBQJDEhc