How to fix Samsung Note 3 SM-N900 bootloader loop?
You have two ways of recovering you data:


Boot into fastboot and try to flash custom recovery (like TWRP). It allows making partition backups, which you can open on PC later.

fastboot flash recovery recovery.img

Try to boot into temporary custom recovery and do the same (full partition backup). However, this depends on device and can be not available for Samsung Note.

Check this and this tutorial.


What concerns fixing the tablet in general from bootloop, it depends on what you've done/what have happened, and probably cannot be achieved without loosing your data. To be on the safe side, it's always preferable to do the backup prior to any manipulations.