speaker sound is low

@minaramrak88067 you are not telling us much about what you have already tried and checked. Also, how low is low. It is good to know if you can still hear it or just barely. It could be a dirty speaker mesh or a bad speaker. Commonly to check for this type of error you will need to start by cleaning the opening for the speaker with a stiff nylon brush (something like a new toothbrush) and see if that works. If not, then it is most likely time to replace the speaker. Since iFixit does not yet have a guide for this, use something like this video right up to 7:04. Then proceed to remove the speaker shown at 8:12. Replacement speakers are readily available at many online stores.

Now, if a new speaker does not resolve it, it is possible that the headphone jack is shorted out and that would mean you need to replace the charging board (daughter board) that has the headphone jack on it. Anything after that will be connected to the audio circuitry on your PCB and would require the schematics and the right tools to perform a boardlevel repair. Start by cleaning and replacing the speaker.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same issues with their phone. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!