I note your question is tagged with just self-defence - what I explain here can be applied whether you are practicing an established martial art or just a bunch of self defence type moves.
There is an exercise in a number of Japanese arts (karate, ninjutsu, aikido and more) called Tai Sabaki. It involves doing the same repeated sequence of moves (whatever is chosen at the time, not like kata) while pivoting at the start of the sequence. Here is an introductory Yotube link, you can explore from there. The purpose of the exercise is to turn and face - or in your case deflect and face - so you are off the original line of attack, giving you a better angle to defend from.
In general though you want to avoid meeting the opponent head on. You can meet them head on if your technique is good, but this can take some training to master. For example, rather than delivering a mae geri (front kick) to the thigh from directly in front of them as they charge, you will have far more success if you step on a 45 degree angle and deliver the kick from there - this is what tai sabaki teaches you.
You will also find that Aikido specifically has ways of dealing with this, many of its throws are based on using the opponents momentum as part of a throw (once again this involves turning as you execute a movement, just like tai sabaki). If you are a practitioner of a striking oriented system you can still practice aikido - you will find it complements whatever you are currently training in and expands your arsenal of moves while teaching you better positioning and movement.