my loved oneMRI report shows that he has edema around optic chiasma which causing pressure on pituitary gland?

If it’s edema, you might try having the person increase their water intake.
Edema (water retention) is caused when you don’t drink enough water. I know it sounds contradictory, but please continue.
When you don’t drink enough water, the body gets dehydrated and the cells don’t receive the nutrients they need for proper function. When the body senses a water shortage, it will start rationing the water to inject into the cells. To do this, it needs to store extra water, but to do this, it has to store extra salt since salt retains water.
The correct way to get rid of edema is to increase the water intake and reduce or quit the salt temporarily so it can flush out the excess salt. Some doctors prescribe diuretics to reduce water retention, but they don’t remove the excess salt,and so the body will continue to store the water until this salt is removed.

You need to get the name of the tumor. Edema is swelling with fluid.

Pituitary tumors are 99.8% not cancer. So that is not the factor. What has to be done now is to determine what type of tumor it is – and that is done via lots and lots of lab tests. After the type is known, then treatment is known – medication(s) or surgery.
When you know the exact size and the type, treatment will be known. If it is touching his optic chiasm, then surgery may be done to debulk the tumor. It there is pressure, it may be that he has pseudotumor cerebri, but again, you don’t have enough details.
Many of the pituitary tumors can now be treated with medications. Surgery is via the nose. Make sure you get the most experienced surgeon you can find. Experience matters a lot here. I just met someone with a botched surgery – you really really want a good surgeon.