1. Install Mobileuncle MTK Tool or Android MTK Engineering
2. Open Mobileuncle MTK Tool or Android MTK Engineering and select Engineer Mode
3. Select Engineer Mode MTK
4. Swap to Hardware Testing
5. Select Audio
6. Select Loudspeaker Mode
7. Here you will find Max Volume Value 128, Change this to 145 and press set.
8. You can set this value up to 160 but above 150 is not recommended else it may damage your speaker.
9. Now you can close Mobileuncle MTK Tool.