What can i do bro , please guide me 
Are you following any charging practice bro? also how is your usage? what are the top apps you normally use? you can check that in battery settings page.
Average usage tha bro . I went iplant they just reinstall os bro idha aprm problem varadhula bro
What cycle will i follow bro i just follow 20 -to 80+ or 90+
Some time 15 to 80+ or 90+
Good to know bro. charging practice porutha varaikum 20% varumbothu charge pannura practice follow pannunga. upto 80% or 100% or in between you can charge to any level as you need bro. I am sure you watched our iPhone battery health tips video.
Those two tips are enough to maintain it over period of months bro. Use the device normally and it will be maintained. We cannot freeze the reduce completely, but gradually it will reduce.