how to boost my battery maximum capacity to 100 percent

It is not possible to "boost" battery capacity in any way. The Maximum Capacity moves in only one direction......down.

The only time that you will ever have 100% Maximum Capacity is the period of time immediately after you replace the battery. From that point on, the Maximum Capacity will start to decline.

Your Battery Capacity is relative to when your device was new, a newer device will result in higher capacity. The more you use your device, the more the battery will age and capacity will decrease. When you use your iPhone, it will go through charge cycles, your iPhone model should retain 80 percent of their original capacity at 500 complete charge cycles under ideal conditions.

25 charge cycle is roughly 1% of battery capacity for your iPhone model, when your battery capacity reaches 80% or below, Apple recommends you replace it.

iPhone battery and performance information --> iPhone Battery and Performance - Apple Support

Tips to extend battery lifespan --> Batteries - Maximizing Performance - Apple

Please see: iPhone Repair & Service - Apple Support