Hi Sabine Schnabeltier,
The K22F bootloader can be found from the KBOOT2.0, you can download KBOOT2.0 from this link:
https://www.nxp.com/webapp/Download?colCode=NXP_KINETIS_BOOTLOADER_2_0_0&appType=license&Parent_node...
After you download it, you can find the bootloader code from folder:
NXP_Kinetis_Bootloader_2_0_0\NXP_Kinetis_Bootloader_2_0_0\targets
Just use the debugger or programmer download the bootloader code to your chip.
Wish it helps you!
Have a great day,
Kerry
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