Unfortunately, you can't. They wont cohabitate and will fight until one is killed.
You would need a very large tank to allow two male betas to co-habitate. Its far more successful to have multiple females together, although they can also become aggressive. I've had 3 males living in my 55 gallon tank, but it had lots of plants and about 25 tetras (glo-fish)
Keep adding them until you find two that like each orher.
Check Google. There are some rare circumstances when you can have two Bettas together.
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