The Fire tablets are based on the Android OS and that hasn't supported Flash for at least 2 years. It may be possible to get a copy of Flash Player onto your Fire, but I couldn't say for sure. Many companies have moved on to HTML now.
Inform the supplier of the video it is unable to be seen. It is their loss if they do not change it. Or view it on a PC.
Flash was abandoned in 2012 because it is completely rubbish and inappropriate for a mobile device. Apple never used Flash because of this - it’s surprising how that Apple standard has become mainstream.
It ***** the life out of your battery, is full of security holes, and slows your device down.