iphone 11 pro max's volume.

Hi,

My phone volume is having some trouble like when i tired to display a video, from the start, the sound is normal and i could hear it with the normal volume that i have set, but suddenly, the sound was getting lower to the point that i couldn't hear it at all, and even if i try to reset it to the max volume, it still has the lowest sound. then next few minute, it started getting normal then another few minute, it was getting trouble again. so, is there any solution in helping me solving this? thank you.