Initially, try to wear them before a competition. The leather will be made to your leg and so will soften.
You can also help them with a jar of milk or cream for the leather (you can buy them everywhere), it will nourish the leather and allow it to soften if your boots are new or they haven't been worn for a long time.
Then for the maintenance of your boot I advise you to pass a soft blow of brush to remove the sand and the probable projections of mud (it will avoid that your leather is damaged and does harden) after each use. Clean them thoroughly with a damp sponge. Be careful, avoid using glycerine soap ... Indeed, it will soften your boot but far too much. Glycerin soap is made for bridle leather. If you put too much, your boot will slip on your leg (like a sock) and the elastic of your boot (if any) will completely relax. Believe me, I made the mistake of doing this and my boots no longer hold ...
Also if your boots are very wet (due to rain or other), fill the paper with newspaper and allow the paper to absorb moisture. Do not put them against a radiator, the leather of your boots may harden.
A little shake: and HOP! your boots will be beautiful and comfortable
I meant Mink Oil* it will stretch supple and soften the boot leather. water may dry it out - i would never dunk any of my $400 tall boots into a bucket of water tbh but in warmer areas i could see how thatd be the preferred method hahha