How to fix 2 wires into this plug?
Make sure the power is off, then cut the plug off and use wire nuts or your country's preferred type of splice. Junctions inside an appliance do not require additional boxes. Since both wires on the fan are black the motor must be isolated so a good frame connection would be my recommendation for a ground unless the frame is plastic then it won’t matter.
There are small 1/8” spade or male disconnects that could be crimped onto the fan wires but there is a chance these could fall out and any male plug will require a splice so I would remove the plug and splice for a good connection.