Needing a simple fix for loading TPU
Loading TPU/TPE can be particularly challenging because many printer loading scripts run too fast for the soft flexible filament to effectively purge whatever normal filament you were using before. A couple tips:


Load with a slightly higher temp than either the TPU or previous filament require, so as to minimize the melt viscosity and reduce the force required.
Make a custom gcode file that contains a slower loading routine: wait for heat, then advance the extruder at a very slow rate for a long distance. Then you just "print" this gcode file whenever you need to load TPU.


However, simply being able to load is not necessarily enough. Not all extruders can reliably print flexible filaments, period. The larger the gap between the pinch wheel and inlet to the hot end, the more likely the filament is to buckle and come out the side. You need to make sure this gap is as short as possible. If there is more than a couple mm of gap, you'll need to make gap-filler or print yourself a new extruder designed for flexibles.

Printing slow and without major velocity changes can help, too. Use relatively low layer heights and low, constant feedrates so the extruder doesn't have to run fast or change pressure often. 

Harder flexible filaments will be easier to print if your setup is borderline. Ninjaflex is one of the hardest to print because it is relatively soft. Semi-flex type filaments are much easier to print if your hardware isn't set up optimally.