The question you asked is directly combined with the concept of saññā(identification).
From the day we born in this world, we sense things around us and recognize them according to the external world. For example, when you first see an object like chair, you don't have any idea that it is a chair. But the knowledge you get from the outside, lead you to believe that it is a chair. So, next time you see a similar shape, you understand that is also a chair.
That's how conventional world is built. But actually, what we see is not what exists. Everything in this universe is made of 4 fundamental things patavi,aapo ,thejo and wayo. Nothing is beyond that.Anything you see from your eyes is just a combination of these 4 elements.Only the outer appearance differs according to the element percentages.
As an example if you consider water => aapo is the dominant factor...
for a rock => patavi is the dominant factor. The names you use for them are just set of words nothing more.
When you consider about the body, first thing you need to know is, the name "body" is just a word. What you feel when you touch yourself and what you see from the mirror is just a combination of 4 factors mentioned above.
In the Buddhism human body is beautifully described. Human body is made of 32 parts.
Head hair, Body hair, Nails, Teeth, Skin
(Kesa, Loma, Nakkha, Danta, Taco)
Flesh, Sinews, Bones, Bone Marrow, Kidneys
(Masam, Naharu, Atthi, Atthiminjam, Vakkam)
Heart, Liver, Diaphragm, Spleen, Lungs
(Hadayam, Yakanam, Kilomakam, Pihakam, Papphasam)
Large Intestine, Small Intestine, Stomach, Feces, Brain
(Antam, Antagunam, Udariam, Kerisam, Mattagunam)
Bile, Phlegm, Pus, Blood, Sweat, Fat
(Pittam, Semhan, Pubbo, Lohitam, Sedo, Medo)
Tears, Grease, Saliva, Mucus, Oil of the Joints, Urine
(Assu, Vasa, Kelo, Singhanika, Lasika, Muttam)
Imagine you separate each of these from your body and see them individually. If you see these things separately, you don't consider them as a body or a human.You might recognize them as blood, piece of bone or piece of flesh etc.
But when they are together you recognize it as the body. That is the wrong saññā(identification).
Body never exist anywhere in the future,past or present. Only these 32 parts where there. If you go deeper you might realize each of these part is just combination of patavi,aapo,thejo and wayo. So ultimately, what really exists is 4 fundamentals, not anything else.
when you realize what you see from the mirror is not your body and just combination of four fundamentals.You will not recognize it as body and you will see it as a combination.
patavi is toughness it belongs to land.. everything in your body made of patavi will decay and added up to soil one day.
aapo is the liquidity and it belongs to ocean.. everything in your body made of aapo will wash away and collect to the ocean.
thejo is the temparature inside the body.. it will mix with the atmosphere once you dead and add to the fire.
wayo is the air inside the body and it will mix to the atmosphere and blow away with the wind..
So if you cannot control these four factors,obviously you cannot control a combination of them as well. So there is no point of telling "body" is mine.
correct your saññā(identification) about the "body" according to Buddhism then you will see the truth.