How can I improve hair density my both temple corners hair thinning and looking frizzy?

This requires an in-person evaluation. I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options and answer any questions you have about supplements. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

At your age, you should begin with having a complete CBC done by your physician to make sure there is no other health issues that is causing the rapid hair loss.  Some hair loss is normal, especially at certain time of the year.  A very promising therapy for shedding and thinness of hair is cold laser hair therapy.  A good one on the market right now is LaserCap which uses 224 cold laser, FDA certified, for thinning and hair loss. 

Consult with a qualified expert in hair loss- only a full examination will help determine the source of your problem.

I'd suggest seeing a hair specialist to review your exact diagnosis and to discuss treatment.  The most likely diagnoses for someone with a story similar to yours is early genetic hair loss as well as hairline maturation. See your physician to confirm and to review all the options.

Your biggest enemy is the progressive thinning leading to a
balding pattern that is not evident at this point in time. The degree of
thinning that you are experiencing would suggest that you should see a
doctor who most likely will get Bulk Measurements of your hair to
determine the degree of the thinning that you are presently having. If the
diagnosis is early genetic hair loss (the most common cause of hair loss
in young men), then the best treatment would be the drug finasteride which
is highly effective in men of your age and may not only stop the hair loss
but possibly reverse it. If you are developing a more advanced balding
pattern the best test to get will determine the Bulk Measurements of your
hair and this will show, over a one-year time frame, how effective the
treatment will be. Once you know this information, then you and your
doctor need to develop a MASTER PLAN which will define what you need to do
over the years to come.