The brilliant thing about parkrun is you can make it what you want - you can go flat out and compare to your fastest time, you can go easy and chat with fellow parkrunners or, as I encourage the runners I coach, you can use it as training, for example...

Try running 4k comfortable then blast the last km as fast as you can

Try gradually building speed so each km is faster than the one before

Try running alternate km hard and easy - 1k hard, 1 easy, 1 hard, 1 easy then finish with 1k hard.

Have a play so it can fit into your training.