If you're using a permissioned chain, the miner computing power is not relevant, because the distributed consensus is based on mining diversity of signed blocks, rather than proof-of-work.
If your chain is permissionless, i.e. with anyone-can-mine=true, then the difficulty for the proof-of-work will automatically adjust in the same way as bitcoin. You can mine externally using GPUs/ASICs in exactly the same way as for bitcoin mining, but otherwise there's no way to increase the miner's computing power beyond that of the physical server it's running on.
