How to mine first block of POS coin
POS coins are not mined in the traditional sense. See, mining is a way to make people expand some energy so no one person can defeat the network by generating fake blocks and appending them to change transaction history. Miners are usually rewarded coins.

See even in POW, the coins aren't mined, they are just generated and awarded to the person who solved the computation. The get the reward because they had to expend some energy to maintain the network
So you see, even in POW, the coins aren't really mined are they?

For POS, you can do an ICO and stake some coins to active wallets. Those people can then begin to use the system. You literally generate coins and issue them out and force people into this staking system in order to make any transaction on the network. Of course, we still haven't solved the distribution issue facing human kinds economic system.

Satoshi did give us a start however.