If you want to spend money on tools, the crimping die you want is something like this:
This crimping die ($18) grabs the two tabs on your connector and fold them in so their tips are pointed inwards/down, as opposite to just wrapping one on the top of the other.
Note there are two sets of tabs on each pin: the rear one is supposed to be crimped to the insulation and act as strain relief while the smaller ones are what bites/crimps the exposed wire.
The crimping tool looks like this ratcheting one. You can buy a bunch of different dies and swap them to fit your needs. As someone said earlier, for a one-off it does not make sense (tool plus one single die ~$50), but I have those for more than a decade and they still deliver crimps that look like what you see used by factory in cars. I think they beat the quintessential "pig-tail" you find at auto parts stores, which is then attached to the old wire with a splice of sorts.
