5Kw Premium Industrial Fan Heater 3 phase https://www.amazon.co.uk/dp/B01MG57ND9/ ... iAb10802DB
Thanks in advance!
If you have just the usual 230V mains supply, then you will certainly not be able to use a three phase powered heater. You can only try to get your money back from Amazon.
The normal mains supply is fused at 13A max at the plug, and a 5KW heater will draw over 20A from a single phase supply.
If you do have a three phase supply available, then it should be simple to find the appropriate plug for 3ph sockets. Can you post photos of the business ends of the various plugs and sockets you have ?