Hello Laura,
Thank you for reaching out to Intel FPGA Community.
For MTBF calculation, you can refer to below link:
How do I calculate the Mean Time between Failure (MTBF) for Altera... (intel.com)
You can find the FIT rate for Altera® devices in the Reliability Report (PDF) which can be downloaded through Resource & Documentation Center (intel.com). You will need CNDA to download the Reliability Report as it is Intel confidential information.
Please revert to us back if you have any questions.
Regards,
Aqid Ayman